# Patent

## Title
Multi-mode charging of hierarchical anode

## Abstract

One aspect of the present invention provides an electrochemical cell system comprising at least one electrochemical cell configured to be connected to a power supply to recharge the cell. The electrochemical cell system comprises a plurality of electrodes and electrode bodies therein. The electrochemical cell system further comprises a switching system configured to permit modifications of the configuration of anodes and cathodes during charging of the electrochemical cell, and a controller configured to control the switching system. The controller is configured to selectively apply the electrical current to a different number of said electrode bodies based on at least one input parameter so as to adjust a rate and density of the growth of the electrodeposited metal fuel.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application claims priority to U.S. Provisional Application Ser. No. 61/414,579 filed on Nov. 17, 2010, the entirety of which is incorporated herein by reference.


FIELD OF THE INVENTION
The present invention relates to a rechargeable electrochemical cell system.
BACKGROUND OF THE INVENTION
Electrochemical cells are well known. An electrochemical cell includes an anode or fuel electrode at which a fuel oxidation reaction takes place, a cathode or oxidant electrode at which an oxidant reduction reaction takes place, and an ionically conductive medium for supporting the transport of ions. In some metal-air cells, such as those disclosed in U.S. patent application Ser. No. 12/385,489 (published as U.S. Patent Application Publication No. 2009/0284229) and Ser. No. 12/901,410 (published as U.S. Patent Application Publication No. 2011/0086278), both of which are incorporated herein by reference, the fuel electrode comprises a plurality of scaffolded electrode bodies, on which metal fuel is reduced and electrodeposited.
Electrochemical cell systems may comprise a plurality of electrochemical cells. In some such electrochemical cell systems, the fuel electrode of the first cell may be coupled to a first terminal, the oxidant electrode of each cell within the cell system may be connected to the fuel electrode of the subsequent cell, and the oxidant electrode of the last cell in the series may be connected to a second terminal. Thus, a potential difference is created within each individual cell, and because these cells are coupled in series, a cumulative potential difference is generated between the first and second terminals. These terminals connect to a load L, creating a potential difference that drives current.
Among other things, the present application endeavors to provide a more efficient and effective architecture for recharging and discharging electrochemical cells and electrochemical cell systems.
SUMMARY OF THE INVENTION
According to an embodiment of the present disclosure, an electrochemical cell includes a fuel electrode comprising a series of permeable electrode bodies arranged in spaced apart relation, an oxidant electrode spaced apart from the fuel electrode, and a charging electrode selected from the group consisting of (a) the oxidant electrode, (b) a third electrode spaced from the fuel electrode and the oxidant electrode, and (c) a portion of the fuel electrode. The electrochemical cell further includes an ionically conductive medium contacting the electrodes, and a charge/discharge controller coupled to a plurality of the electrode bodies of the fuel electrode. The charge/discharge controller is configured to apply an electrical current between the charging electrode and at least one of the permeable electrode bodies, with the charging electrode functioning as an anode and the at least one permeable electrode body functioning as a cathode, such that reducible metal fuel ions in the ionically conductive medium are reduced and electrodeposited as metal fuel in oxidizable form on the at least one permeable electrode body, so that said electrodeposition causes growth of the metal fuel among the permeable electrode bodies, with the electrodeposited metal fuel establishing an electrical connection between the permeable electrode bodies. The charge/discharge controller is configured to selectively apply the electrical current to a different number of said permeable electrode bodies, each functioning as a cathode, based on at least one input parameter so as to adjust a rate and density of the growth of the electrodeposited metal fuel.
According to another embodiment of the present disclosure, a method of recharging an electrochemical cell is provided. The electrochemical cell includes a fuel electrode comprising a series of permeable electrode bodies arranged in spaced apart relation, an oxidant electrode spaced apart from the fuel electrode, and a charging electrode selected from the group consisting of (a) the oxidant electrode, (b) a third electrode spaced from the fuel electrode and the oxidant electrode, and (c) a portion of the fuel electrode. The electrochemical cell further includes an ionically conductive medium contacting the electrodes, and a charge/discharge controller coupled to a plurality of the electrode bodies of the fuel electrode. The charge/discharge controller is configured to apply an electrical current between the charging electrode and at least one of the permeable electrode bodies, with the charging electrode functioning as an anode, and the at least one permeable electrode body functioning as a cathode, such that reducible metal fuel ions in the ionically conductive medium are reduced and electrodeposited as metal fuel in oxidizable form on the at least one permeable electrode body, so that said electrodeposition causes growth of the metal fuel among the permeable electrode bodies with the electrodeposited metal fuel establishing an electrical connection between the permeable electrode bodies. The charge/discharge controller is configured to selectively apply the electrical current to a different number of said permeable electrode bodies based on at least one input parameter so as to adjust a rate and density of the growth of the electrodeposited metal fuel.
The method includes selecting, based on the at least one input parameter, between a higher density progressive growth mode and a higher rate growth mode. The method further includes charging the electrochemical cell based on the selected one of the higher density progressive charge mode and the higher rate growth mode. In the higher density progressive growth mode, said charging comprises applying the electrical current to a terminal one of the permeable electrode bodies, with the charging electrode functioning as the anode and the terminal electrode body functioning as the cathode, such that the reducible metal fuel ions are reduced and electrodeposited as metal fuel in oxidizable form on the terminal permeable electrode body. The electrodeposition causes growth of the metal fuel among the permeable electrode bodies such that the electrodeposited metal fuel establishes an electrical connection between the terminal electrode body and each subsequent permeable electrode body with said reduction and deposition occurring on each subsequent permeable electrode body upon establishment of said electrical connection. In the higher rate growth mode, said charging comprises applying the electrical current simultaneously to a plurality of said electrode bodies, with the charging electrode functioning as the anode and each of the plurality of electrode bodies functioning as cathodes, such that the reducible metal fuel ions are reduced and electrodeposited as metal fuel in oxidizable form on the terminal permeable electrode body, said electrodeposition causing growth of the metal fuel among the permeable electrode bodies. The method further includes disconnecting the electrical current to discontinue the charging.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a cross-sectional view of an electrochemical cell system that includes two electrochemical cells;
FIG. 2 illustrates an exploded view of the electrochemical cell system of FIG. 1;
FIG. 3 illustrates an electrode holder of one of the electrochemical cells of FIG. 1;
FIG. 4 illustrates the electrode holder of FIG. 3, holding a fuel electrode and a plurality of spacers connected to the electrode holder
FIG. 5 illustrates one of the spacers of FIG. 4 in greater detail;
FIG. 6 illustrates a connection between the spacers of FIG. 5 and the electrode holder of FIG. 3 in greater detail;
FIG. 7 schematically illustrates electrical connections between the electrochemical cell and an external load or power supply according to an embodiment of a cell system in accordance with the present invention;
FIG. 8 schematically illustrates electrical connections between the electrochemical cell and an external load or power supply according to an embodiment of a cell system in accordance with the present invention;
FIG. 9 schematically illustrates a switching system according to an embodiment of the cell system of FIG. 8;
FIG. 10 schematically illustrates a switching system according to another embodiment of the cell system of FIG. 8;
FIG. 11 schematically illustrates a switching system according to another embodiment of the cell system of FIG. 8;
FIGS. 12A-C schematically illustrate the embodiments of FIGS. 9-11 further comprising a plurality of cells a switching system according to another embodiment of the cell of FIG. 8;
FIG. 13 schematically illustrates a switching system similar to the embodiment of FIG. 11, further comprising a controller;
FIG. 14 shows a flowchart illustrating an embodiment of a method of charging the cell, in accordance with the present invention;
FIG. 15 shows a flowchart illustrating an embodiment of a method of discharging the cell;
FIG. 16 schematically illustrates a switching system according to another embodiment of the cell of FIG. 8; and,
FIG. 17 shows a flowchart illustrating an embodiment of an algorithm for charging the cell, in accordance with the present invention.



DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS OF THE INVENTION
FIGS. 1 and 2 illustrate an electrochemical cell system 100 that includes two electrochemical cells 10 according to an embodiment of the invention. As illustrated, each cell 10 includes a fuel electrode 12, and an oxidant electrode 14 that is spaced from the fuel electrode 12. The fuel electrode 12 supported by an electrode holder 16. The electrochemical system 100 also includes a cover 19 that is used to cover the electrochemical cells 10 on one side of the system 100, while one of the electrode holders 16 is used to cover the opposite side of the system 100, as illustrated in FIG. 1.
In an embodiment, the fuel electrode 12 is a metal fuel electrode that functions as an anode when the cell 10 operates in discharge, or electricity generating, mode, as discussed in further detail below. In an embodiment, the fuel electrode 12 may comprise a plurality of permeable electrode bodies 12a-d, such as screens that are made of any formation able to capture and retain, through electrodepositing, or otherwise, particles or ions of metal fuel from an ionically conductive medium that circulates in the cell 10, as discussed in further detail below. Components of the cell 10, including for example, the fuel electrode 12, the permeable electrode bodies 12a-d thereof, and the oxidant electrode 14, may be of any suitable construction or configuration, including but not limited to being constructed of Nickel or Nickel alloys (including Nickel-Cobalt, Nickel-Iron, Nickel-Copper (i.e. Monel), or superalloys), Copper or Copper alloys, brass, bronze, or any other suitable metal. In an embodiment, a catalyst film may be applied to some or all of the permeable electrode bodies 12a-d and/or the oxidant electrode 14, and have a high surface material that may be made of some of the materials described above. In an embodiment, the catalyst film may be formed by techniques such as thermal spray, plasma spray, electrodeposition, or any other particle coating method.
The fuel may be a metal, such as iron, zinc, aluminum, magnesium, or lithium. By metal, this term is meant to encompass all elements regarded as metals on the periodic table, including but not limited to alkali metals, alkaline earth metals, lanthanides, actinides, and transition metals, either in atomic, molecular (including metal hydrides), or alloy form when collected on the electrode body. However, the present invention is not intended to be limited to any specific fuel, and others may be used. The fuel may be provided to the cell 10 as particles suspended in the ionically conductive medium. In some embodiments, a metal hydride fuel may be utilized in cell 10.
The ionically conductive medium may be an aqueous solution. Examples of suitable mediums include aqueous solutions comprising sulfuric acid, phosphoric acid, triflic acid, nitric acid, potassium hydroxide, sodium hydroxide, sodium chloride, potassium nitrate, or lithium chloride. The medium may also use a non-aqueous solvent or an ionic liquid. In the non-limiting embodiment described herein, the medium is aqueous potassium hydroxide. In an embodiment, the ionically conductive medium may comprise an electrolyte. For example, a conventional liquid or semi-solid electrolyte solution may be used, or a room temperature ionic liquid may be used, as mentioned in U.S. patent application Ser. No. 12/776,962 (published as U.S. Patent Application Publication No. 2010/0285375), the entirety of which is incorporated herein. In an embodiment where the electrolyte is semi-solid, porous solid state electrolyte films (i.e. in a loose structure) may be utilized.
The fuel may be oxidized at the fuel electrode 12 when the fuel electrode 12 is operating as an anode, and an oxidizer, such as oxygen, may be reduced at the oxidant electrode 14 when the oxidant electrode 14 is operating as a cathode, which is when the cell 10 is connected to a load L and the cell 10 is in discharge or electricity generation mode, as discussed in further detail below. The reactions that occur during discharge mode may generate by-product precipitates, e.g., a reducible fuel species, in the ionically conductive medium. For example, in embodiments where the fuel is zinc, zinc oxide may be generated as a by-product precipitate/reducible fuel species. The oxidized zinc or other metal may also be supported by, oxidized with or solvated in the electrolyte solution, without forming a precipitate (e.g. zincate may be a dissolved reducible fuel species remaining in the fuel). During a recharge mode, which is discussed in further detail below, the reducible fuel species, e.g., zinc oxide, may be reversibly reduced and deposited as the fuel, e.g., zinc, onto at least a portion of the fuel electrode 12 that functions as a cathode during recharge mode. During recharge mode, either the oxidant electrode 14 or a separate charging electrode 70 (which may be of similar construction or configuration as permeable electrode bodies 12a-d in some embodiments), and/or another portion of the fuel electrode 12, as described below, functions as the anode. The switching between discharge and recharge modes is discussed in further detail below.
The electrode holder 16 defines a cavity 18 in which the fuel electrode 12 is held. The electrode holder 16 also defines an inlet 20 and an outlet 22 for the cell 10. The inlet 20 is configured to allow the ionically conductive medium to enter the cell 10 and/or recirculate through the cell 10. The inlet 20 may be connected to the cavity 18 via an inlet channel 24, and the outlet 22 may be connected to the cavity 18 via an outlet channel 26. As illustrated in FIG. 3, the inlet channel 24 and the outlet channel 26 may each provide a meandering tortuous path through which the ionically conductive medium may flow. The meandering path defined by the inlet channel 24 preferably does not include any sharp corners in which the flow of the medium may become stagnated or in which any particulates in the medium may collect. As discussed in further detail below, the length of the channels 24, 26 may be designed to provide an increased ionic resistance between cells that are fluidly connected in series.
For each cell 10, a permeable seal member 17 may be bonded between sealing surfaces on the electrode holders 16 and/or the cover 19, as appropriate, to enclose at least the fuel electrode 12 in the cavity 18. The seal member 17 also covers the inlet and outlet channels 24, 26. The seal member 17 is non-conductive and electrochemically inert, and is preferably designed to be permeable to the ionically conductive medium in the orthogonal direction (i.e., through its thickness), without permitting lateral transport of the ionically conductive medium. This enables the ionically conductive medium to permeate through the seal member 17 for enabling ion conductivity with the oxidant electrode 14 on the opposing side to support the electrochemical reactions, without “wicking” the ionically conductive medium laterally outwardly from the cell 10. A few non-limiting examples of a suitable material for the seal member 17 are EPDM and TEFLON®.
In the illustrated embodiment, the cavity 18 has a generally rectangular, or square, cross-section that substantially matches the shape of the fuel electrode 12. The cavity 18 may be connected to the inlet channel 24 by a plurality of inlets 34 so that when the ionically conductive medium and precipitates or reducible fuel species enter the cavity 18, the ionically conductive medium and fuel are distributed along a side of the fuel electrode 12. In some embodiments, one side of the cavity 18, specifically, the side of the cavity 18 that is connected to the inlet channel 24, may include a plurality of fluidization zones, such as is described in U.S. patent application Ser. No. 12/901,410, incorporated herein in its entirety by reference. In other embodiments, the ionically conductive medium may enter the cavity 18 through a diffuser, such as is described in U.S. Provisional Patent Application No. 61/301,377, now converted into U.S. patent application Ser. No. 13/019,923 (published as U.S. Patent Application Publication No. 2011/0189551), each of which is also incorporated herein in its entirety by reference. In various embodiments, the ionically conductive medium may flow in parallel or in series through a plurality of cells 10. In some embodiments, the ionically conductive medium may utilize a combination of parallel and series flows. Furthermore, in various embodiments the ionically conductive medium may flow at a varying rate, and even may flow intermittently (i.e. static for a time) during operation of the one or more cells 10.
As illustrated in FIG. 4, a plurality of spacers 40, each of which extends across the fuel electrode 12 in a spaced relation to each other, may be connected to the electrode holder 16 so that the fuel electrode 12 may be held in place relative to the electrode holder 16 and to the oxidant electrode 14. In an embodiment, the plurality of permeable electrode bodies 12a-12d, as illustrated in FIG. 2, may be separated by sets of the plurality of spacers 40, so that each set of spacers 40 is positioned in between adjacent electrode bodies to electrically isolate the electrode bodies 12a-12d from each other. Within each set of spacers 40 between adjacent electrode bodies, the spacers 40 are positioned in a spaced relation in a manner that creates so-called “flow lanes” 42 therebetween, as discussed in greater detail below. The flow lanes 42 are three-dimensional and have a height that is substantially equal to the height of the spacers 40. In an embodiment, the spacers 40 may be provided by a single frame that has cut-outs corresponding to the flow lanes. In an embodiment, the flow lanes 42 may include a foam or honeycomb-type structure that is configured to allow the ionically conductive medium to flow therethrough. In an embodiment, the flow lanes 42 may include an array of pins that are configured to disrupt the flow of the ionically conductive medium through the flow lanes. In an embodiment, the frame, spacers 40, flow lanes 42, and/or other elements of cell 10 may be defined by plastic formed by injection molding, or epoxy/insulating material formed using chemical processes. The illustrated embodiment is not intended to by limiting in any way.
The spacers 40 are non-conductive and electrochemically inert so they are inactive with regard to the electrochemical reactions in the cell 10. The spacers 40 are preferably sized so that when they are connected to the electrode holder 16, the spacers 40 are in tension, which allows the spacers 40 to press against the fuel electrode 12, or one of the electrode bodies 12a-12c, so as to hold the fuel electrode 12 or bodies thereof in a flat relation relative to the electrode holder 16. The spacers 40 may be made from a plastic material, such as polypropylene, polyethylene, noryl, fluoropolymer, etc. that allows the spacers 40 to be connected to the electrode holder 16 in tension. In various embodiments, the spacers 40 may be attached together by techniques such as (but not limited to) thermal bonding, chemical bonding, or ultrasonic welding/bonding
In the embodiment illustrated in FIG. 5, each spacer has an elongated middle portion 44, and a shaped connecting portion 46 at each end. The shaped connecting portions 46 are configured to be held by openings 48 having substantially similar shapes in the electrode holder 16, as illustrated in FIG. 6. In the illustrated embodiment, the shaped portions 46 and the openings 48 have a substantially triangular shape, although the illustrated shape is not intended to be limiting in any way. The substantially triangular shape provides surfaces 50 on opposite sides of the elongated portion 44 of the spacer 40 that are configured to contact corresponding surfaces 52 on the electrode holder 16. Because the surfaces 50, 52 are angled with respect to a major axis MA of the elongated portion 44 of the spacer 40 and the tension in the spacer 40 will be along the major axis MA, the forces created by the tension may be distributed across a larger surface, as compared to a shaped portion having a circular or square shape with the same area.
Once the spacers 40 have been connected to the electrode holder 16 via the end portions 46, the flow lanes 42 are defined across the cavity 18 of the electrode holder 16. The spacers 40 are configured to essentially seal off one flow lane 42a from an adjacent flow lane 42b, that is separated by one of the spacers 40 so that the ionically conductive medium is guided to generally flow in substantially one direction. Specifically, the ionically conductive medium may generally flow in a first direction FD across the fuel electrode 12, from the inlet channel 24 to the outlet channel 26. A suitable pressure drop is generated between the inlet channel 24 and the inlets 34 so that the ionically conductive medium may flow across the cavity 18 and to the outlet channel 26, even when the cell 10 is oriented such that the flow is substantially upward and against gravity. In an embodiment, the ionically conductive medium may also permeate through the fuel electrode 12, or an individual permeable electrode body 12a-12d, in a second direction SD and into a flow lane that is on the opposite side of the fuel electrode 12 or permeable electrode body 12a-12d. 
As illustrated in the embodiment of FIG. 7, the fuel electrode 12 of cell 10 in electrochemical cell system 100 may be selectively connected to an external load L so that electrons given off by the fuel as the fuel is oxidized at the fuel electrode 12 may flow to the external load L. A switching system 60 comprising a plurality of switches, may selectively electrically connect each of the individual permeable electrode bodies 12a-12d of the fuel electrode 12, and may also selectively connect the permeable electrode bodies 12a-12d to the oxidant electrode 14. As shown, in some embodiments electrochemical cell system 100 may further comprise other cells 10. In an embodiment, the switching system 60 may comprise a terminal selector system 62 configured to couple or decouple the external load L for use in discharging the cell 10, or couple or decouple a power supply PS for use in charging the cell 10. In another embodiment the switching system 60 and the terminal selector system 62 may be separate, but may, in an embodiment, communicate with each other. The switching system 60 is discussed in greater detail below.
The oxidant electrode 14 functions as a cathode when the oxidant electrode 14 is connected to the external load L and the cell 10 operates in discharge mode. When functioning as a cathode, the oxidant electrode 14 is configured to receive electrons from the external load L and reduce an oxidizer that contacts the oxidant electrode 14. The oxidizer may be any species of the oxidant available for oxidation at the charging electrode. For example, the species may be a free ion, or an ion bonded to or coordinated with other ions or constituents in the ionically conductive medium. In an embodiment, the oxidant electrode 14 comprises an air breathing electrode and the oxidizer comprises oxygen in the surrounding air.
The oxidizer may be delivered to the oxidant electrode 14 by a passive transport system. For example, where oxygen present in ambient air is the oxidizer, simply exposing the oxidant electrode 14 to ambient air via openings in the cell, such as the openings that are provided by grooves 54 in the cover 19 and grooves 56 in the electrode holder 16 provided in the center of the electrochemical cell system 100, may be sufficient to allow diffusion/permeation of oxygen into the oxidant electrode 14. Other suitable oxidizers may be used and embodiments described herein are not limited to the use of oxygen as the oxidizer. A peripheral gasket 15 may be positioned between the periphery of the oxidant electrode 14 and the cover 19 or electrode holder 16, as appropriate, to prevent the ionically conductive medium from leaking around the oxidant electrode 14 and into the area in the grooves 54, 56 for air exposure.
In other embodiments, a pump, such as an air blower, may be used to deliver the oxidizer to the oxidant electrode 14 under pressure. The oxidizer source may be a contained source of oxidizer. In an embodiment, the oxygen may be recycled from the cell 10, such as is disclosed in U.S. patent application Ser. No. 12/549,617 (published as U.S. Patent Application Publication No. 2010/0119895), incorporated in its entirety herein by reference. Likewise, when the oxidizer is oxygen from ambient air, the oxidizer source may be broadly regarded as the delivery mechanism, whether it be passive or active (e.g., pumps, blowers, etc.), by which the air is permitted to flow to the oxidant electrode 14. Thus, the term “oxidizer source” is intended to encompass both contained oxidizers and/or arrangements for passively or actively delivering oxygen from ambient air to the oxidant electrode 14.
Electricity that can be drawn by the external load L is generated when the oxidizer at the oxidant electrode 14 is reduced, while the fuel at the fuel electrode 12 is oxidized to an oxidized form. The electrical potential of the cell 10 is depleted once the fuel at the fuel electrode 12 is entirely oxidized or oxidation is arrested due to passivation of the fuel electrode. A portion of the switching system 60 may be positioned in between the oxidant electrode 14 and the load L so that the oxidant electrode 14 may be connected and disconnected from the load L, as desired. Again, more details about the switching system 60, and the electrical configuration thereof, is provided below.
To limit or suppress hydrogen evolution at the fuel electrode 12 during discharge mode and during quiescent (open circuit) periods of time, salts may be added to retard such a reaction. Salts of stannous, lead, copper, mercury, indium, bismuth, or any other material having a high hydrogen overpotential may be used. In addition, salts of tartrate, phosphate, citrate, succinate, ammonium or other hydrogen evolution suppressing additives may be added. In an embodiment, metal fuel alloys, such as Al/Mg may be used to suppress hydrogen evolution. Other additives may also or alternatively be added to the ionically conductive medium, including, but not limited to additives which enhance the electrodeposition process of the metal fuel on the fuel electrode 12, such as is described in U.S. Provisional Patent Application 61/304,928, now converted into U.S. patent application Ser. No. 13/028,496, incorporated in its entirety herein by reference. After the fuel in the cell 10 has been entirely oxidized, or whenever it is desirable to regenerate the fuel within the cell 10 by reducing oxidized fuel ions back to fuel, the fuel electrode 12 and the oxidant electrode 14 may be decoupled from the external load L and coupled to a power supply PS. As noted above, such connections may be made, for example, with the use of the switching system 60 and the terminal selector system 62.
The power supply PS is configured to charge the cell 10 by applying a potential difference between the fuel electrode 12 and the oxidant electrode 14 such that the reducible species of the fuel is reduced and electrodeposited onto at least one of the permeable electrode bodies 12a-12d and the corresponding oxidation reaction takes place at the oxidant electrode 14, which is typically oxidation of an oxidizable species to evolve oxygen, which may be off-gassed from the cell 10. In an embodiment wherein oxygen is the oxidant, oxygen ions in an aqueous electrolytic solution are oxidized. The oxygen ions may be available from an oxide of the fuel (e.g., ZnO when zinc is the fuel), hydroxide ions (OH−), or water molecules (H2O). As described in detail in U.S. patent application Ser. No. 12/385,489, which has been incorporated herein by reference, in an embodiment only one of the permeable electrode bodies, such as 12a, is connected to the power supply PS so that the fuel reduces onto the permeable electrode body and progressively grows to and on the other permeable electrode bodies 12b-12d, one by one. The switching system 60 may control how the permeable electrode bodies 12a-12d and the oxidant electrode 14 participate in the electrochemical reactions of the cell, as is described in greater detail below.
FIG. 8 shows an embodiment where a separate charging electrode 70 of cell 10 in electrochemical cell system 100 is provided to function as the charging electrode, rather than the oxidant electrode 14. Again, in some embodiments other cells 10 may be part of electrochemical cell system 100, as shown. As illustrated in FIG. 2, the separate charging electrode 70 may be positioned between the fuel electrode 12 and the oxidant electrode 14, with a spacer 72 and the seal member 17 being positioned between the separate charging electrode 70 and the oxidant electrode 14. The spacer 72 is non-conductive and has openings through which the ionically conductive medium may flow.
In the embodiment described above with respect to FIG. 7, the oxidant electrode 14 functions as the cathode during power generation/discharge, and as the anode during charging, as described above. In FIG. 8, the oxidant electrode 14 remains the cathode during power generation/discharge, but may be disconnected during charging, while the separate charging electrode 70 is connected to the power supply PS to function as the anode. During current generation, the fuel on the fuel electrode 12 is oxidized, generating electrons that are conducted to power the load L and then conducted to the oxidant electrode 14 for reduction of the oxidizer (as discussed in more detail above). In embodiments comprising the separate charging electrode 70, the switching system 60 may control how the permeable electrode bodies 12a-12d the oxidant electrode 14, and the separate charging electrode 70 participate in the electrochemical reactions of the cell, as is described in greater detail below.
It is also possible in any of the embodiments of the invention to apply the cathodic potential to any or all of the electrode bodies 12a-12d of the fuel electrode 12, rather than to just one to produce body-by-body progressive growth. Progressive growth emanating from one terminal is advantageous because it provides more density of the electrodeposited fuel. Specifically, the growth in the previously connected electrode bodies continues as each subsequent body is connected by the progressing growth. This and other advantages are discussed in greater detail in U.S. patent application Ser. No. 12/385,489, which has been incorporated herein by reference. With all the electrode bodies subject to the same potential, the growth will only occur until a short occurs between the charging electrode, which is the oxidant electrode 14 in the embodiment of FIG. 7 and the separate charging electrode 70 in the embodiment of FIG. 8, and the electrode body proximate to it. Thus, it is possible to have a faster, but less dense, growth in this manner, which may be amenable to certain re-charging needs.
The embodiments illustrated in FIGS. 7 and 8 should not be considered to be limiting in any way and are provided as non-limiting examples of how the cell 10 may be configured to be rechargeable. The recharge mode of the present invention, in the context of the switching system 60, is discussed in greater detail below. As another example, U.S. patent application Ser. No. 12/885,268 (published as U.S. Patent Application Publication No. 2011/0070506), filed on Sep. 17, 2010, the entire content of each of which is incorporated herein by reference, describes embodiments of a rechargeable electrochemical cell system with charge/discharge mode switching in the cells.
Returning to FIG. 4, after the ionically conductive medium has passed through the fuel electrode 12, the medium may flow into the outlet channel 26 that is connected to the outlets 36 of the cavity 18 of the electrode holder 16 and the outlet 22. The outlet 22 may be connected to the inlet 20 in embodiments where the medium is recirculated in the cell 10, or to an inlet of an adjacent cell, as discussed in further detail below, when a plurality of cells 10 are fluidly connected in series. In an embodiment, the outlet 22 may be connected to a vessel to collect the medium that has been used in the cell 10. Again, in various embodiments the flow of the ionically conductive medium may vary, for example by flowing through a plurality of cells 10 in series or parallel, at a constant rate or a varying rate, continuously or intermittently.
The cells 10 illustrated in FIGS. 1 and 2 may be fluidly connected in series. Details of embodiments of cells that are connected in series are provided in U.S. patent application Ser. No. 12/631,484 (published as U.S. Patent Application Publication No. 2010/0316935), filed Dec. 4, 2009 and incorporated herein by reference in its entirety. The outlet 22 of a first cell 10 may be fluidly connected to the inlet 20 of a second cell 10, and the outlet 22 of the second cell 10 may be connected to the inlet 20 of a third cell, and so on. Although the embodiment of FIGS. 1 and 2 illustrates two cells 10, additional cells may be stacked and fluidly connected to the illustrated cells. Due to the meandering, tortuous paths that are created by the inlet channel 24 and the outlet channel 26, described above and illustrated in FIGS. 3 and 4, the length of the flow passageways for the medium via the channels 24, 26 is greater than the distance between the fuel electrode 12 and the oxidant electrode 14 in each of the cells 10. This creates an ionic resistance between the pair of fluidly connected cells that is greater than an ionic resistance within an individual cell 10. This may reduce or minimize internal ionic resistance loss of the stack of cells 100, as discussed in U.S. patent application Ser. No. 12/631,484.
In an embodiment of operation, the fuel electrode 12, which already has metal fuel deposited thereon, is connected to the load L and the oxidant electrode 14 is connected to the load L. The ionically conductive medium enters the inlet 20 under positive pressure and flows through the inlet channel 24, the inlets 34 of the cavity 18, and into the flow lanes 42. The ionically conductive medium flows across the permeable electrode bodies 12a-12d in the flow lanes 42 defined by the elongated middle portions 22 of the spacers 40. The ionically conductive medium may also permeate through the permeable electrode bodies 12a-12d of the fuel electrode 12. The ionically conductive medium simultaneously contacts the fuel electrode 12 and the oxidant electrode 14, thereby allowing the fuel to oxidize and conduct electrons to the load L, while the oxidizer is reduced at the oxidant electrode 14 via the electrons that are conducted to the oxidant electrode 14 by the load L. After the ionically conductive medium has passed through the flow lanes 42, the medium flows out of the cavity 18 via the outlets 36 of the cavity 18, through the outlet channel 24, and out the outlet 22 of the cell 10.
When the potential of the cell 10 has been depleted or when it is otherwise desirable to recharge the cell 10, the fuel electrode 12 is connected to the negative terminal of the power supply PS and the charging electrode, which may be the oxidant electrode 14 or the separate charging electrode 70, is connected to the positive terminal of the power supply PS. Such connections may again be through the switching system 60, discussed below. In the charging or recharge mode, a cathode portion of the fuel electrode 12 becomes the cathode and an anode portion of the fuel electrode 12 and/or the charging electrode 14, 70 becomes the anode, as is described in greater detail below. By providing electrons to a cathode portion of the fuel electrode 12, fuel ions may reduce into fuel and redeposit onto the permeable electrode bodies 12a-12d, as is described in greater detail below, while the ionically conductive medium circulates through the cell 10 in the same manner as described above with respect to the discharge mode.
The flow lanes 42 provide directionality and distribution of the ionically conductive medium across the fuel electrode 12. The flow lanes 42 may also prevent the particulates from settling and/or covering the electrodes. When the cell 10 is in charging mode, the improved distribution of the particulates across the fuel electrode 12 allows for a more uniform deposition of the reduced fuel onto the fuel electrode 12, which improves the density of the fuel on the fuel electrode 12, and increases the capacity and energy density of the cell 10, thereby enhancing the cycle-life of the cell 10. In addition, by having the ability to control the distribution of the precipitates or reaction by-product during discharge, early passivation/deposition of the by-product on the fuel electrode 12 may be prevented. Passivation leads to lower fuel utilization and lower cycle life, which is undesirable.
The examples of FIGS. 1-8 are not limiting, and are provided solely for context to understand general principles of an embodiment of the cells 10 of the cell system 100. Any cell construction or configuration may be used. With an understanding of the cell system provided, attention is turned to the configuration and operation of the switching system 60 of the invention.
As noted, during a charging mode for the cell 10, a potential difference is applied across electrodes in the cell 10. Although either the oxidant electrode 14 or the separate charging electrode 70 generally function as the anode during charging, an anodic potential may be applied to other electrodes, such as some of the electrode bodies in the fuel electrode 12. Likewise, during charging a cathodic potential may be initially applied to electrode body 12a of the fuel electrode 12, but may also be initially applied to one or more of the other permeable electrode bodies 12b-12d of the fuel electrode 12. As such, those permeable electrode bodies 12a-12d of fuel electrode 12 having a cathodic potential behave as a cathode during charge, and serve as a reduction site for a reducible fuel species, such as the oxidized fuel ions created in the cell during discharging.
As the reducible fuel species is reduced on those of permeable electrode bodies 12a-12d having the cathodic potential, the oxidant electrode 14 or the separate charging electrode 70 and/or those of the permeable electrode bodies 12b-12d having the anodic potential will oxidize an oxidizable oxygen species, such as the reduced oxidant species created in the cell during discharging. Thus, when the cell 10 is a metal-air cell, the reducible metal fuel species is being reduced and electrodeposited on some of the permeable electrode bodies 12a-12d of the fuel electrode 12, and the oxidizable oxygen species is being oxidized to oxygen gas, which may be off-gassed from the cell 10. In this embodiment, those electrodes and electrode bodies having an anodic potential may be considered an oxygen evolving electrode (OEE).
To determine which of the electrodes (i.e. permeable electrode bodies 12a-d, the oxidant electrode 14 and/or the separate charging electrode 70) have anodic potentials or cathodic potentials during charging, electrical connections therebetween may be controlled by the switching system 60, as is discussed in greater detail below.
It may be advantageous to the fuel growth for the potential difference used to charge the cell 10 to be applied between adjacent bodies in the cell 10, such that an electrode body having the anodic potential is adjacent to an electrode body having the cathodic potential. Once sufficient fuel growth has occurred on the electrode body having the cathodic potential, the electrode having the anodic potential may change, so that the permeable electrode body that previously was part of a set of electrode bodies having an anodic potential may become part of a set of electrode bodies having the cathodic potential. In an embodiment wherein there are N permeable electrode bodies, the application of the anodic potential from the power source to permeable electrode bodies 2 to N and the charging electrode may comprise connecting all of the electrode bodies plus the charging electrode together at the same time, then disconnecting each of electrode bodies 2 to N in order. Alternatively, in an embodiment, the application of the anodic potential from the power source to permeable electrode bodies 2 to N and the charging electrode could comprise connecting and disconnecting each of the electrode bodies and the charging electrode individually in order (such that electrode body 2 is connecting to the anodic potential, then is disconnected and electrode 3 is connected to the anodic potential, and so on until the charging electrode is finally connected to complete the growth).
In an embodiment, the charging electrode may merely be the last electrode to receive the anodic potential during charging. For example, the charging electrode could be the oxidant electrode or a separate electrode. When the charging electrode is a separate electrode, it could have a specialized construction different from the electrode bodies of the fuel electrode, or could be the same as the permeable electrode bodies (i.e. just one more electrode body), but for the fact that growth of the fuel during charging does not continue past it.
In the above-described embodiment illustrated in FIGS. 1-2, the progressive changing of which electrode(s) have the anodic potential may follow the fuel growth through each of the permeable electrode bodies 12a-12d, so that an electrode having an anodic potential remains the electrode body spaced adjacent to an electrode having the cathodic potential. As shown in the embodiments of the following Figures, the switch system 60 may be configured to selectively connect and disconnect the various electrodes and electrode bodies to maintain the adjacent positions of the anodic potential and the cathodic potential.
FIGS. 9-12 show embodiments of the switching system 60 of the cell 10. The cell 10 is connectable to the power supply PS, the load L, or to other cells 10 in series, through a first terminal 130 and a second terminal 140, wherein the first terminal 130 is negative (cathodic) during recharging, and the second terminal 140 is positive (anodic) during recharging. As shown, the cell 10 has a fuel electrode 12 comprising permeable electrode bodies 12a-12d, a charging electrode 70, and an oxidant electrode 14. In an embodiment, the plurality of switches may selectively couple at least some of the permeable electrode bodies 12b-12d to a power source, such as power supply PS, for application of an anodic potential during a recharging mode of the cell 10, in which a cathodic potential is applied to at least electrode body 12a, as will be described in greater detail below.
In FIG. 9, the switching system 60 includes a bypass switch 150, configured to provide a direct connection between the first terminal 130 and the second terminal 140. The bypass switch 150 may be similar to that described in U.S. patent application Ser. No. 12/885,268, which has been incorporated herein in its entirety by reference. A cell 10 can be bypassed with bypass switch 150 for a number of reasons that affect the performance of the stack.
For example, a short between charging electrode 70 and the electrode bodies 12a-12d having a cathodic potential during charge (detected by voltage measurement as described below) may lead to expense of parasitic power during charge. An electrical short may lead to a sudden drop in voltage between the charging and fuel electrodes as the current is shunted between the charging and fuel electrodes. Another example is during discharge, where any cell 10 that has a higher kinetic or ohmic loss affects the round trip efficiency and discharge power of the stack. Also, consumption of fuel in the cell 10 during discharge earlier than other cells 10 can lead to voltage reversal in the cell 10 and stack power loss, and can be prevented by bypassing the cell 10 when the discharge voltage falls below a critical value. Complete consumption of zinc or other fuel during discharge leads to a sudden drop in voltage between the fuel and oxidant electrodes. Any other criteria to detect the performance of cells 10 may be used, and the examples herein are not limiting. Certain cells 10 may not meet performance requirements (for example, maximum power during discharge) due to yield issues and problems related to fabrication and assembly of electrodes. These cells 10 can be permanently placed in bypass mode. Other cells 10 may meet performance requirements initially, however may have cycle life issues and can be placed in bypass mode after the performance falls below a required limit. Thus, bypassing a cell 10 through bypass switch 150 provides an option to increase reliability and performance of the stack.
The switching system 60 of FIG. 9 also includes an oxidant electrode switch 160 associated with the oxidant electrode 14. The oxidant electrode switch 160 would be closed during discharge, so that an electric potential across the fuel electrode 12 and the oxidant electrode 14 may allow a current to be drawn by a load L connected between the first terminal 130 and the second terminal 140, which during discharge would have positive and negative polarities respectively.
A charging electrode switch 170 may be associated with the charging electrode 70, such that the charging electrode 70 may be electrically connected to the second terminal 140 when the power supply PS is connected between the first terminal 130 and the second terminal 140. As discussed below, the charging electrode 70 may not always have an anodic potential applied to it, and in an embodiment may only have an anodic potential when fuel growth between it and electrode body 12d is desired. Also shown are switches 180, 190, and 200, associated with electrode bodies 12b-12d respectively, all of which are configured to connect electrode bodies 12b-12d to the second terminal 140 as well.
As was noted, it is advantageous that an electrode having an anodic potential be adjacent to an electrode having a cathodic potential, so that growth on the electrode having the cathodic potential is enhanced. Such enhancement may, for example, include greater density of fuel growth than if the electrode having the anodic potential is further from the closest electrode having the cathodic potential (i.e. if a neutral electrode separates the electrodes having the anodic and cathodic potentials). This enhanced density may be due to the initial dendrites that first contact the anodic body being disrupted because they lack sufficient cross-section to carry the current between the anodic and cathodic bodies. That is, they burn off similarly to a fuse element subject to excess current. This delays shorting between the anodic and cathodic bodies, which takes place when the density has increased further to provide dendrites of sufficient cross-sectional area (individually and/or collectively) to enable the current conduction without disruption. Another advantage may be lower electrolyte IR loss in configurations where the distance between the charging electrode 70 and the fuel electrode 12 is lower, as compared to configurations wherein the electrode having the anodic potential is further from the closest electrode having the cathodic potential (i.e. where neutral electrodes separate the electrodes having the anodic and cathodic potentials). This IR efficiency advantage resulting from less distance between anodic and cathodic electrodes may be realized both in embodiments where metallic growth is occurring between the electrodes and in other embodiments, such as a metal hydride fuel where the hydrogen ions are being reduced.
To achieve progressive modification of which electrodes have the anodic potential, to account for shifts between electrodes having an anodic potential versus electrodes having a cathodic potential, the cell 10 in the charging mode would be configured such that the bypass switch 150 is open, so that current does not bypass the cell 10. Because the cell is in a charging mode, the oxidant electrode switch 160 is also open, so that the oxidant electrode 14 is electrically disconnected from the cell 10. Since initially fuel growth is desired on electrode body 12a, only electrode body 12a is electrically connected to first terminal 130, applying the cathodic potential thereto. To establish an anodic potential on the electrode body adjacent to electrode body 12a, at least electrode body 12b will be electrically connected to second terminal 140. To achieve this electrical connection in the illustrated embodiment, at least switch 180 is closed. In an embodiment, electrode bodies 12c-12d, and charging electrode 70 may also be electrically connected to second terminal 140, and thus may also have the anodic potential. Because of the potential difference between the electrode(s) having the anodic potential (i.e. initially electrode body 12a) and the electrode(s) having the cathodic potential (i.e. initially at least electrode body 12b), reducible fuel species in the ionically conductive medium may be reduced at the electrode having the initial cathodic potential (electrode body 12a) while cations in the ionically conductive medium are oxidized at electrode body 12b (and any other body/electrode to which the anodic potential is applied).
Once fuel growth on the electrodes having the cathodic potential progresses to a certain point, for example, to the point where an electrical connection is formed between the electrode(s) having the cathodic potential and the electrode(s) having the anodic potential, the switching system 60 may disconnect the shorting electrode body that had the anodic potential, such that that electrode body has a cathodic potential applied to it, and a potential difference may be formed again between adjacent electrode bodies. This may require the further electrical connection of the adjacent electrode body to the second terminal 140, if the electrical connection did not already exist, so as to create the anodic potential on that body. For example, in FIG. 9, once fuel growth on electrode body 12a causes a short with electrode body 12b, switch 180 is opened so that both electrode body 12a and, through the electric connection of the fuel growth, electrode body 12b, have the cathodic potential. On the other hand, switch 190 closes (if it was not already closed before), such that at least electrode body 12c has an anodic potential, thus maintaining the adjacent electrode body separation for the potential difference between the electrode(s) having the cathodic potential and the electrode(s) having the anodic potential.
The progressive shifting of which electrodes have the cathodic potential and which electrodes have the anodic potential may continue throughout the cell 10, with the opening of switches 190 and 200, until no further progression is desired or possible. For example, in the illustrated embodiment, wherein there is a separate charging electrode 70, the progression will end when the separate charging electrode 70 is the only electrode body having the anodic potential, and all permeable electrode bodies 12a-12d of the fuel electrode 12 have the cathodic potential. Charging of the cell 10 may subsequently end when fuel growth on electrode body 12d causes an electrical connection between electrode body 12d and charging electrode 70. In an embodiment, the switching system 70 may be configured to have an over-charge configuration, wherein the cell may be configured to selectively apply a cathodic potential to charging electrode 70 by opening switch 170, and closing switch 160, applying the anodic potential to the oxidant electrode 14, utilizing it for further charging of cell 10 by permitting fuel growth on the charging electrode 70.
Charging of the cell 10 may in various embodiments progress from electrode body to electrode body among the plurality of permeable electrode bodies 12a-12d, or may end based on criteria such as the voltage, current, slope of voltage, slope of current, charge capacity, or value of impedance or resistance. Such measurements in various embodiments may be taken over one or more of the electrode bodies 12a-12d, or across one or more cells 10. In an embodiment, charging may end based on a sensing electrode placed between the charging electrode and the last permeable electrode body 12d of the fuel electrode 12.
During discharge of the cell 10 in the embodiment of FIG. 9, oxidant electrode switch 160 would be closed, while charging electrode switch 170 would be open. Additionally, switches 180, 190, and 200 would be open, and fuel consumption would be from electrode body 12d to electrode body 12a, wherein the electrical connection between the electrode bodies 12a-12d are through the fuel growth. In the illustrated embodiment, this is so electrode bodies 12a-12d are not shorted to the oxidant electrode 14 by oxidant electrode switch 160.
Continuing to FIG. 10, another embodiment of switching system 60 is illustrated for the cell 10. Again there is the bypass switch 150, configured to connect first terminal 130 directly to second terminal 140, bypassing the cell 10. The switching system 60 also includes a series of connecting switches 210a-d, configured to selectively and progressively connect each of the electrode bodies 12b-d to either the first terminal 130 or the second terminal 140, such that each of the electrode bodies 12b-d either has a cathodic potential (i.e. is connected to at least electrode body 12a) or an anodic potential (i.e. is connected to at least charging electrode 70). As shown, during charging, bypass switch 150 would be open so the cell is not bypassed. Oxidant electrode switch 160 would also be open, so that oxidant electrode 14 is disconnected during the charging process. Charging electrode switch 170 would be closed so that at least charging electrode 70 would have an anodic potential. To promote minimal distance between the electrode(s) having the cathodic potential (initially just electrode body 12a) and the electrodes having the anodic potential, switches 210b, 201c, and 210d would be closed, so that the anodic potential created through the electrical connection to second terminal 140 is applied through electrode bodies 12b-12d, as well as charging electrode 70. As fuel growth on electrode body 12a progresses, it will eventually contact electrode body 12b. In an embodiment, at that time switch 210b would open, so that electrode bodies 12a-12b have the cathodic potential, while electrode bodies 12c-12d and charging electrode 70 have the anodic potential. In an embodiment, switch 210a would also be closed, so that a stronger electrical connection between electrode bodies 12a-12b is formed, beyond the electrical connection of the fuel growth. Such progression could continue, as above, with the opening of switches 210c and 210d respectively, as the number of electrode bodies having the anodic potential shrinks, while the number of electrodes having the cathodic potential grows. Again, in some embodiments switches 210b and 210c could close in progression, to form a stronger electrical connection between electrode bodies 12a-12d as the number of electrodes having a cathodic potential progressively grows.
During discharge of the cell 10 in the embodiment of FIG. 10, oxidant electrode switch 160 would be closed, while charging electrode switch 170 would be open. In an embodiment switches 210a-210d could remain open and fuel consumption would be from electrode body 12d to electrode body 12a, wherein the electrical connection between the electrode bodies 12a-12d are through the fuel growth. In another embodiment, switches 210a-210d could be closed, so that an electrical connection is between all electrode bodies 12a-12d of the fuel electrode 12, and fuel is oxidized throughout the fuel electrode 12 while an oxidant is reduced at the oxidant electrode 14. This is permissible in this embodiment because opening switch 170 also prevents the electrode bodies 12a-d from being shorted to the oxidant electrode 14 by oxidant electrode switch 160.
Another embodiment of the switching system 60 for the cell 10 is seen in FIG. 11. Once more, the switching system 60 comprises the bypass switch 150, configured to selectively connect the first terminal 130 directly to the second terminal 140, in order to bypass the cell 10. The switching system 60 of the embodiment of FIG. 11 also includes another series of connecting switches 220a-d, configured to selectively connect each of the electrode bodies 12a-d to the charging electrode 70. Again, the switching system 60 may be configured to allow progressive change of those electrodes having the cathodic potential (i.e. at least electrode body 12a) and those electrodes having the anodic potential (i.e. at least charging electrode 70). As shown, during charging, bypass switch 150 would be open so the cell is not bypassed. Oxidant electrode switch 160 would also be open, so that oxidant electrode 14 is disconnected during the charging process. Charging electrode switch 170 would be closed so that at least charging electrode 70 would have an anodic potential. Switch 220a would be opened so that the cell is not bypassed from first terminal 130 to second terminal 140 through switch 220a and switch 170. To promote minimal distance between the electrode(s) having the cathodic potential (initially just electrode body 12a) and the electrodes having the anodic potential, at least switch 220b would be closed, so that at least electrode bodies 12b, as well as charging electrode 70, have the anodic potential. As fuel growth on electrode body 12a progresses, it will eventually contact electrode body 12b. In an embodiment, at that time switch 220b would open, so that electrode bodies 12a-12b have a cathodic potential (connected through the fuel growth). Switch 220c would then close, if it was not closed before, so that at least electrode body 12c, as well as charging electrode 70, would have the anodic potential. Such progression could continue, as above, with the opening of switches 210c and 210d respectively, as the number of electrode bodies having the anodic potential shrinks, while the number of electrode bodies having the cathodic potential grow.
During discharge of the cell 10 in the embodiment of FIG. 11, oxidant electrode switch 160 would be closed, while charging electrode switch 170 would be open. In an embodiment switches 220a-220d could remain open and fuel consumption would be from electrode body 12d to electrode body 12a, wherein the electrical connection between the electrode bodies 12a-12d are through the fuel growth therebetween.
The progressive shifting of which electrode bodies have a cathodic potential versus which electrode bodies have an anodic potential may be analogized as the cell 10 having N electrode bodies defining two conceptual electrodes, a cathodic potential electrode and an anodic potential electrode. In the cell, the constituent makeup of the cathodic potential electrode may begin with a single electrode body, while the anodic potential electrode may comprise at least the adjacent electrode body, up to all other electrode bodies. During charging, fuel grows on the cathodic potential electrode until, for example, no further growth on the electrode body is possible (i.e. the cathodic potential electrode has shorted to the anodic potential electrode). At that time, the electrode body of the anodic potential electrode that is adjacent to the cathodic potential electrode is reassigned to become part of the cathodic potential electrode, through an electrical connection formed by the fuel growth and/or through the use of electrical circuitry or switches associated with the electrode bodies of the cell. With the reassignment, the cathodic potential electrode now comprises two electrode bodies, while the anodic potential electrode has one less than its initial number of electrode bodies. As a potential difference may resume between the cathodic potential electrode and the anodic potential electrode, fuel growth from charging may resume, again until, for example, no further growth on the electrode bodies of the cathodic potential electrode is possible.
The progressive shifting of the constituent makeup of the cathodic potential electrode and the anodic potential electrode may continue throughout the cell, for example with the opening and/or closing of switches associated with the electrode bodies, until no further progression is desired or is possible. For example, once the anodic potential electrode comprises only a single electrode body, no further progression is possible. The charging of the cell may subsequently end when fuel growth on the cell causes an electrical connection to form between the conceptual cathodic potential electrode and the conceptual anodic potential electrode that comprises only a single electrode body.
Again, in various embodiments charging of the cell 10 may progress from electrode body to electrode body among the plurality of permeable electrode bodies 12a-12d, or may end based on criteria such as the voltage, current, slope of voltage, slope of current, charge capacity, or value of impedance or resistance. Such measurements in various embodiments may be taken over one or more of the electrode bodies 12a-12d, or across one or more cells 10. In an embodiment, charging may end based on a sensing electrode placed between the charging electrode and the last permeable electrode body 12d of the fuel electrode 12.
As noted previously, in an embodiment, multiple electrochemical cells 10 may be combined in cell system 100. Shown in FIGS. 12A-C are electrochemical cell systems 100 of the embodiments of FIGS. 9-11, however comprising N electrochemical cells 10. The number N is any integer greater than or equal to two, and is not limited to any particular number. As illustrated, the bypass switches 150 in the switching systems 60 of each cell 10 are configured to selectively bypass each cell 10 by providing a direct connection between the first terminal 130 and the second terminal 140. Such a connection may again be used to bypass defective cells 10, or for any other reason. Also, in various embodiments of cell systems 100, different embodiments of the switching system 60 (such as those found in FIGS. 9-11) may be used in conjunction with one another in a single cell system 100.
In any embodiment, the switches of the switching system 60 (or any other switch described herein) may be of any type, and the term switch is broadly intended to describe any device capable of switching between the modes or states described. For example, in some non-limiting embodiments, the switches may be single pole single throw or single pole double throw. They may be of the pivoting, sliding or latching relay type. Also, semiconductor based switches may be used as well. The switches may be activated electrically (electromechanical relay) or magnetically or by other methods known to those familiar in the art. Any other suitable type of switch may be used, and the examples herein are not limiting. In an embodiment, the plurality of switches may be connected in series if the switch has a leakage current in one direction. For example, the body diode of a MOSFET semiconductor based switch will conduct in one direction and the leakage current can be eliminated by placing MOSFET semiconductor based switches facing back to back in series.
Any suitable control mechanism may be provided to control the action of switches in the switching system 60 and/or the terminal selector system 62. As shown in FIG. 13, in an embodiment the switches of the switching system 60 may be controlled by a controller 230. The controller 230 may be of any construction and configuration. In an embodiment, the controller 230 may be configured to manage application of the anodic potential from the power supply PS to permeable electrode bodies 12b-d and the charging electrode 70. The controller 230 may cause electrodeposition of metal fuel, through reduction of reducible ions of the metal fuel from the ionically conductive medium, to progressively grow from permeable electrode body 12a to each subsequent electrode body 12b-d for application of a cathodic potential to each subsequently connected electrode body 12b-d. The controller 230 may also cause removal of the anodic potential from each subsequently connected electrode body, and may cause application of the anodic potential to at least the subsequent electrode body unconnected by the electrodeposition, or the charging electrode where the last electrode body (i.e. electrode body 12d) has been electrically connected by the electrodeposition to the prior electrode bodies 12a-c. Such application of the anodic potential may be configured to permit or cause oxidization of an oxidizable species of the oxidant.
In an embodiment, the controller 230 may comprise hard-wired circuitry 232 that manipulates the switches based on an input 234 determining the proper switch configuration. The controller 230 may also include a microprocessor for executing more complex decisions, as an option. In some embodiments, the controller 230 may also function to manage connectivity between the load L and the power source and the first and Nth cells (i.e. may control the terminal selector system 62 described above). In some embodiments, the controller 230 may include appropriate logic or circuitry for actuating the appropriate bypass switches 150 in response to detecting a voltage reaching a predetermined threshold (such as drop below a predetermined threshold). In some embodiments, the controller 230 may further comprise or be associated with a sensing device 236, including but not limited to a voltmeter (digital or analog) or potentiometer or other voltage measuring device or devices, that can be used to determine when to modify the configuration of the plurality of switches, such as to maintain the proximity of the anode and the cathode as fuel growth progresses during charging. In some embodiments, the sensing device 236 may instead measure current, resistance, or any other electrical or physical property across or of the cell 10 that may be used to determine when to modify the configuration of the plurality of switches. For example, the sensing device 236 may measure a spike in current or a drop in potential difference between two electrode bodies. In some embodiments, the controller 230 may control the switches of the switching system 60 based on the passage of increments of time. For example, in an embodiment the time for fuel growth to progress between adjacent electrode bodies may be known, and used to calculate when to operate the switching system 60 so as to progressively rewire the electrodes to maintain an adjacent separation between the anode and the cathode. In an embodiment, the controller 230 may control the switches of switching system 60 to provide a high efficiency mode for the cell, such as is disclosed in U.S. Provisional Patent Application 61/323,384, now pending as U.S. patent application Ser. No. 13/083,929, each of which is incorporated in its entirety herein by reference.
In some embodiments, the controller 230 may be configured to selectively enter different charging modes. For example, in one mode a plurality of electrode bodies may initially have an anodic potential, but the number decreases as the electrode bodies are given a cathodic potential. In another mode, only a single electrode body has an anodic potential at any given time, and the electrode body with the anodic potential changes as prior electrode bodies are given the cathodic potential. For example, in the former mode, the controller 230 may close all switches associated with the charging electrode 70 and electrode bodies 12b-d during recharge, such that an anodic potential is applied to each of electrode bodies 12b-d and the charging electrode 70. The controller 230 may then progressively open the switches associated with each of electrode bodies 12b-d as the electrode bodies 12b-d progressively become electrically connected to electrode body 12a, and thus have a cathodic potential. In the latter mode, the controller may initially close only the switch associated with electrode body 12b, giving electrode body 12b an anodic potential while electrode body 12a has a cathodic potential. When fuel growth on electrode body 12a reaches electrode body 12b, creating an electrical connection therebetween, the controller 230 may open the switch associated with electrode body 12b that gave electrode body 12b the anodic potential, such that electrode body has a cathodic potential through its electrical connection to electrode body 12a. The controller 230 may then proceed to close the switch associated with electrode body 12c, to provide electrode body 12c with the anodic potential, again creating a potential difference, and the progression of fuel growth. These progressions of switch reassignments by the controller 230 may continue through or until only the charging electrode 70 has the anodic potential, as is described above.
As seen in FIG. 14, another aspect of the present invention may include a method 240 for charging the electrochemical cell 10. Again, electrochemical cell 10 comprises the fuel electrode 12 comprising the plurality of permeable electrode bodies 12a-d. Although four permeable electrode bodies are listed, any number greater than or equal to two are possible. The cell 10 further includes the oxidant electrode 14, and the charging electrode, which may be the oxidant electrode 14 or the separate charging electrode 70. The cell 10 additionally includes the ionically conductive medium, and the switching system 60 comprising a plurality of switches, wherein at least some of the plurality of switches are associated with one of the permeable electrode bodies 12a-d, the oxidant electrode 14, and the charging electrode (i.e. oxidant electrode 14 or separate charging electrode 70). During a charging mode, reducible fuel ions in the ionically conductive medium are reduced and electrodeposited as fuel in oxidizable form on a cathode comprising at least permeable electrode body 12a while an oxidant is oxidized on an anode comprising at least an adjacent one of the permeable electrode bodies 12b-d and/or the charging electrode (i.e. charging electrode 70).
The method 240 starts at 250, and includes at 260 electrically connecting the cathode (i.e. in an embodiment, initially just permeable electrode body 12a), distal from the charging electrode, to the negative terminal of power supply PS, and the anode (i.e. initially at least permeable electrode body 12b) to the positive terminal of the power supply PS, creating a potential difference therebetween. The method 240 continues at 270, wherein, the fuel is electrodeposited on the cathode (i.e. at least permeable electrode body 12a). As seen in step 280, the method 240 may continue by determining if fuel growth has progressed to beyond a threshold amount. In an embodiment the threshold amount may be ascertained when the cell 10 is shorted by the fuel growth creating an electrical connection through the fuel growth between the cathode (i.e. permeable electrode body 12a) and the anode (i.e. permeable electrode body 12b). As shown, if fuel growth has not reached the threshold amount, the growth of fuel at 270 is repeated. Once the threshold amount is reached, the method continues at 290, wherein it may be determined if further fuel growth is both possible and desired. In an embodiment, the determination at 290 may include ascertaining if there are additional electrode bodies, such as permeable electrode bodies 12c-d, that fuel growth may be possible on. If so, the method continues at 300 by using the plurality of switches of the switching system 60 to disconnect the connecting electrode body (i.e. permeable electrode body 12b) from the anode, and if it were not connected through the switching system 60 before, connecting the next adjacent electrode body (i.e. permeable electrode body 12c) to the anode. This creates the potential difference between the cathode (now comprising permeable electrode bodies 12a-b) and the anode (comprising at least permeable electrode body 12c). The method 240 then returns to 270 wherein fuel growth continues on the cathode. If no further fuel growth is possible or desired at 290, the method 240 continues to 310 by disconnecting at least the negative terminal of the power source PS from the cell 10 to discontinue the charging process. The method 240 may then end at 320.
Shown in FIG. 15, another aspect of the present invention may include a method 330 for discharging the electrochemical cell 10, which may be similar to that described above as related to FIG. 14. During the discharge mode, fuel on permeable electrode bodies 12a-12d is oxidized (and thus is consumed into the ionically conductive medium as reducible fuel ions), while an oxidizer is reduced at the oxidant electrode 14.
The method 330 starts at 340, and includes at 350 using the plurality of switches of the switching system 60 to connect the permeable electrode bodies 12a-d that contain fuel. In an embodiment, if the cell 10 is completely charged all permeable electrode bodies 12a-d would be electrically connected to one another. As the cell 10 is in discharge mode, the plurality of switches of the switching system 60 would be configured to electrically disconnect the separate charging electrode 70 (if present). In an embodiment, the method 330 would continue at 360 by electrically connecting the cathode (i.e. the air cathode, oxidant electrode 14) to the negative terminal of load L, and the anode (i.e. the fuel electrode 12, containing the electrically connected permeable electrode bodies 12a-d) to the positive terminal of the power supply PS, creating a potential difference therebetween. The method 330 continues at 370, wherein the fuel is consumed on the fuel electrode 12. In an embodiment, because the plurality of switches 60 connect the permeable electrode bodies 12a-d, an anodic potential is applied to each of the permeable electrode bodies 12a-d, and fuel may be consumed from each or any of permeable electrode bodies 12a-d. As seen in step 380, the method 330 may continue by determining if consumable fuel has been depleted from any permeable electrode body 12a-d. In an embodiment, a sensor, such as the sensing device 236 above, which may include a current or a voltage sensor, may be present in the cell 10, and may indicate when consumable fuel has been depleted from one or more of the permeable electrode bodies 12a-d. If no depletion is detected, the discharging may continue as method 330 returns to step 370. If, however, consumable fuel has been depleted from one or more of permeable electrode bodies 12a-d, then method 330 may continue to step 390, wherein it may be determined whether there are any remaining permeable electrode bodies 12a-d that contain consumable fuel. This determination may be made simultaneously with the determination of depletion in step 380, and may be made through a survey of sensing device(s) 236, or by any other appropriate method.
If consumable fuel remains on one or more of permeable electrode bodies 12a-d, the method 330 may continue at step 400, wherein the switching system 60 adjusts the plurality of switches so that any of permeable electrode bodies 12a-d that lack consumable fuel are disconnected from fuel electrode 12. In an embodiment, consumption of fuel may initially be from the electrode body that is closest to the oxidant electrode 14 (such as, for example, permeable electrode body 12d in the illustrated embodiments above), and switching system 60 may disconnect permeable electrode body 12d, 12c, and 12b in that order, until all fuel is consumed from permeable electrode body 12a. Once none of the permeable electrode bodies 12a-d contain consumable fuel, or further discharging is no longer desired (or possible), the method may continue to step 410, wherein the load L may be disconnected. In an embodiment, the load L may remain connected to the cell 10 when it is depleted, until the cell 10 is recharged, in which case it may be disconnected so that the cell 10 may be connected instead to the power supply PS. The method 330 may then end at 420.
FIG. 16 depicts another embodiment of the cell 10. As shown, the embodiment of cell 10 in FIG. 16 has the fuel electrode 12 with five electrode bodies 12a-e. Cell 10 further has a separate charging electrode 70 (i.e. a dedicated OEE), and an oxidant electrode 14. As in the above embodiments, cell 10 includes a switching system 60 configured to selectively connect these electrodes and electrode bodies to one of the first terminal 130 or the second terminal 140. The switching system 60 may include the controller 230, configured to control the plurality of switches connected to it through circuitry 232. As shown, the controller 230 may have the sensing device 236 included within it. Controller 230 may also receive instructions through the input 234 regarding how to control the switches.
As in the above embodiments, the cell 10 may have the bypass switch 150 configured to connect first terminal 130 directly to second terminal 140, bypassing the cell 10 in cases such as where a fault is present within the cell 10, or for any other reason where utilization of the cell 10 is not desired. The oxidant electrode 14 is again selectively connected to the second terminal 140 for discharging by oxidant electrode switch 160, and the separate charging electrode 70 is again selectively connected to the second terminal 140 for charging by the charging electrode switch 170. In the illustrated embodiment, the electrode bodies 12b-e may be selectively connected to either the first terminal 130 or the second terminal 140 by electrode body switches 425b-e, where “b” through “e” indicate which of electrode bodies 12b-e are associated with the respective switch. As is shown in the illustrated embodiment, electrode body switches 425b-e are configured to alternatively connect each of electrode bodies 12b-e to either a first bus 427a associated with electrode body 12a (and thus first terminal 130), or a second bus 427b associated with the separate charging electrode 70 (and thus second terminal 140 through charging electrode switch 170). In an embodiment, electrode body switches 425b-e may be characterized as Single Pole, Double Throw. In some embodiments, electrode body switches 425b-e may have three alternative settings, such that each electrode body 12b-e may be electrically connected to electrode body 12a (and first terminal 130), separate charging electrode 70, or disconnected from both electrode body 12a and separate charging electrode 70. In an embodiment, such electrode body switches 425b-e may be characterized as Single Pole, Triple Throw.
During charging of the electrochemical cell 10, power is applied from a power supply between first terminal 130 and second terminal 140. Bypass switch 150 would be open so that there is no short between first terminal 130 and second terminal 140. Since the cell 10 is in a charging mode, the oxidant electrode 14 is not utilized, so oxidant electrode switch 160 is also open. Accordingly, during charging the charging electrode switch 170 would be closed. As each of electrode bodies 12b-e may be selectively coupled to the anode or the cathode in this embodiment, charging techniques such as but not limited to the progressive OEE described above, or that disclosed in U.S. Provisional Patent Application No. 61/383,510 and U.S. patent application Ser. No. 13/230,549, each of which is incorporated herein in its entirety by reference, may be utilized. The operation of electrode body switches 425b-e in some embodiments is discussed in greater detail below.
Turning now to the flowchart in FIG. 17, another aspect of the present invention may include an algorithm 430 associated with different charge modes for the electrochemical cell 10. Although description of the operation of the algorithm 430 will be made with reference to the embodiment of the cell 10 in FIG. 16, the algorithm 430 may be implemented onto any suitable embodiment of the electrochemical cell 10 by any appropriate mechanism. In one non-limiting embodiment, instead of utilizing the electrode body switches 425b-e, a more complex multiplexing switching system 60 may be utilized. In another non-limiting embodiment, a plurality of Single Pole, Single Throw switches may be configured in an array to allow for electrical connection or isolation between any two or more of electrode bodies 12a-e and separate charging electrode 70. Any suitable system for electrically connecting electrode bodies 12a-e and/or separate charging electrode 70 may be utilized.
In an embodiment the algorithm 430 may include instructions, such as computer interpretable or readable instructions, that may program or otherwise control the controller 230. In some embodiments, the algorithm 430 may be located on a system that is networked with or otherwise connected to controller 230. In some embodiments, the algorithm 430 may be stored on a medium within controller 230, or within any other controller that may allow programmatic control of the switches in switching system 60.
As shown, algorithm 430 may be configured, at 440, to select a particular charge mode for the cell 10. The selection of the charge mode may be made by any appropriate determination criteria 450. For example, in an embodiment the determination criteria 450 may include measurements 460 of the cell 10. The measurements 460 of the cell 10 may be any appropriate measure of the status of the cell, including but not limited to sensor readings pertaining to the current status of fuel growth on permeable electrode bodies 12a-e, readings of the current electrical connections formed by the switching system 60, measurements of a voltage and/or current from or through the cell 10, or so on. To ascertain measurements 460, controller 230 may utilize sensing device 236, which in the current embodiment shows leads extending across the cell 10, between first terminal 130 and second terminal 140.
Measurements 460 may also include measures of the environment. In one embodiment, measurements 460 of the environment may include ascertaining the current time. For example, where the cell 10 is associated with a solar power system, charging earlier in the day may utilize a different charge mode than charging when the sun is closer to setting. Other measurements 460 of the environment are also possible. For example, in some non-limiting embodiments, measurements 460 may be of the environmental temperature, weather conditions, ambient light, movement of the cell 10 (i.e. if the cell 10 is utilized in a vehicle, different charge modes may be utilized for different speeds or braking styles), or so on.
Determination criteria 450 may also include manual overrides 470, which may include any form of manual selection as to which charge mode is desired. Such a manual selection for manual overrides 470 may, in an embodiment, be provided to the controller 230 by input 234. In an embodiment, determination criteria 450 may also include limits 480, which for example may determine an appropriate charge mode based on exceeding predefined tolerances or settings. For example, limits 480 may be based on the measurements 460, and include, for example, voltage difference between electrodes or electrode bodies, current impedance between electrodes or electrode bodies, or so on. In various embodiments, limits 480 may be based on voltage, current, slope of voltage, slope of current, charge capacity, or value of impedance or resistance, for example. Such limits 480 may be based on measurements 460 on or across one or more electrode bodies 12a-e, or on or across one or more cells 10.
Once the charge mode is selected at 440, the controller 230 may identify the charge mode at 490, and proceed to charge the cell 10 accordingly. Although in an embodiment the charge mode may be one which utilizes a progressive OEE, such as that described above, in the illustrated embodiment the controller 230 is configured to select from two alternative charge modes, a progressive charge mode 500, and a parallel charge mode 600. In other embodiments, additional or alternative charge modes may be utilized, and may be in accordance with the algorithm 430.
As shown in the illustrated embodiment, progressive charge mode 500 is a high capacity charge mode. This implies that the cell 10 is configured to be charged in a manner that provides a significant amount of density in the fuel growth between electrode bodies 12a-e. In some embodiments, this high capacity charge mode may take a longer interval of time to complete the charging process, but may enable the greatest amount of energy storage within the cell 10. Such a charging mode may be useful for a number of applications, including but not limited to emergency backup power and uninterruptible power supplies, where a larger amount of power may be needed, and a relatively large amount of time is available to recharge the cell 10 following its use. In such applications the amount of energy stored in cells 10 is of greater importance than the charging rate. Because the charging process is roughly serial between the electrode bodies of the fuel electrode 12, the charging rate is slower than in other embodiments. In the illustrated embodiment, wherein the cell 10 has five electrode bodies 12a-e in the fuel electrode 12, and a separate charging electrode 70 (i.e. the dedicated oxygen evolving electrode, or OEE), the progressive charging mode 500 may include five phases.
When the cell 10 is uncharged, the progressive charge mode 500 may begin at a first phase 505, wherein only the first electrode body 12a forms the cathode, while electrode bodies 12b-e and the separate charging electrode 70 form the charging electrodes. In the embodiment of FIG. 16, the first phase 505 would have electrode body switches 425b-e connecting electrode bodies 12b-e to the separate charging electrode 70 through second bus 427b, which would be connected to second terminal 140 through charging electrode switch 170. As such, only electrode body 12a would be electrically connected to first terminal 130, creating a potential difference between electrode body 12a and the group of charging electrodes formed by the electrode bodies 12b-e and the separate charging electrode 70. Fuel growth would then proceed on electrode body 12a towards the adjacent electrode body 12b. 
Once the fuel growth reaches a sufficient amount that electrode body 12a and electrode body 12b short together at 510, the progressive charge mode 500 would proceed to a second phase at 515, wherein electrode bodies 12a-b form the cathode, while electrode bodies 12c-e and the separate charging electrode 70 form the charging electrodes. In the embodiment of FIG. 16, the second phase 515 would have electrode body switch 425b disconnect electrode body 12b from the group of charging electrodes on second bus 427b, and electrically connect it to electrode body 12a through first bus 427a. The determination that electrode bodies 12a-b have shorted at 510 may be made through any suitable mechanism. For example, the sensing device 236 associated with controller 230 may measure a voltage drop or a current spike across the cell 10. In other embodiments, other sensing devices 236 may ascertain the electrical connection, indicating the need to proceed to the second phase at 515.
As fuel growth progresses through the cell 10, the progressive charge mode 500 may electrically disconnect the contacting electrode body 12b-e from the second bus 427b, and connect it instead to the first bus 427a, progressively reassigning it form a charging electrode to a cathode. In embodiments wherein electrode body switches 425b-e are Single Pole, Triple Throw, the electrode body switches 425b-e may either be configured to connect contacting electrode bodies 12b-e along first bus 427a, or the electrode body switches 425 b-e may move to their electrically disconnected position, such that their electrical connection to first terminal 130 is through the fuel growth alone. As depicted in the flowchart of FIG. 17, progressive charge mode 500 continues at 520 with determining the shorting of electrode bodies 12b-c, before proceeding to a third phase at 525, where electrode body 12c would be disconnected from electrode body 12d, such as by the throwing of electrode body switch 425c. Fuel growth progresses until the shorting between electrode bodies 12c-d at 530. At that time, a fourth phase would begin at 535, with electrode body 12d being electrically disconnected from electrode body 12e, such as by the throwing of electrode body switch 425d, connecting electrode body 12d with the first bus 427a. At 540, the fuel growth progression to electrically short electrode bodies 12d and 12e is determined, and a fifth phase 545 begins, where electrode body 12e is electrically disconnected from the separate charging electrode 70, such as by the throwing of electrode body switch 425e, connecting electrode body 12e with the first bus 427a, such that none of the charging electrodes 12b-3 are connected to the separate charging electrode 70 through the second bus 427b. 
Once all electrode bodies 12b-e are connected with electrode body 12a, by the fuel growth through electrode bodies 12a-e and/or electrical connections through the first bus 427a, the fuel may continue to grow on electrode body 12e towards the separate charging electrode 70, due to the potential difference between those electrodes. Eventually, at 550, it may either be determined that electrode body 12e has shorted with the separate charging electrode 70, indicating maximum fuel growth throughout the cell 10, or a threshold charge capacity has been reached. Such a threshold capacity may be defined so that the cell does not “over-charge.” For example, in some embodiments it may be undesirable that fuel growth reach and form an electrical connection to the separate charging electrode 70. In an embodiment, the threshold charge capacity may be approximately 80-100% of the maximum possible charge capacity for the cell 10. The measurement of capacity may be made by any suitable mechanism, including in some embodiments taking measurements with the sensing device 236, or computing or estimating a charge capacity through controller 230. Regardless, once the threshold capacity has been reached, or electrode body 12e has shorted with the separate charging electrode 70, the cell may enter an idle state, to await a future discharge mode.
If during the selection of the charge mode at 440, a desire for a faster charge is indicated, the parallel charge mode 600 may be selected at 490. In the parallel charge mode 600, mini-cells may be formed within the cell 10, with alternating bodies between electrode body 12a and the separate charging electrode 70 acting as either an anode or a cathode. In an embodiment, the parallel charge mode 600 may be N times faster than progressive charge mode 500 (where N is the number of electrode bodies that metal fuel is being plated on). In an embodiment, the growth rate on a given electrode body is limited by the diffusion-limited current density of the metal fuel deposition, which is affected by a number of factors, including viscosity, concentration, diffusity, and so on. Although the parallel charge mode 600 would be faster than the progressive charge mode 500, the fuel growth may be potentially less dense than in the progressive charge mode 500, because the total charge deposited is limited by the time taken for electrical connections to form between all electrode bodies. In some embodiments, the energy density held by the cell 10 charged by the parallel charge mode 600 may be 1⁄4 to 1⁄2 that of the cell 10 charged by the progressive charge mode 500. Some examples of applications that would prefer the parallel charge mode 600 may include, for example, electric vehicles such as forklifts or cars, where a faster charge rate may be of greater importance than a larger charge density, like when the vehicle is being continuously used in close proximity to charging opportunities.
In an embodiment, the parallel charge mode 600 may begin at a first phase 605, with electrode bodies 12a, 12c, and 12e connected to the first terminal 130, while electrode bodies 12b and 12d, as well as the separate charging electrode 70, are connected to the second terminal 140. In the embodiment of FIG. 16, to connect electrode bodies 12c and 12e to the first terminal 130, such that electrode bodies 12a, 12c, and 12e are the initial cathodes during charging, electrode body switches 425c and 425e may initially be controlled to connect electrode bodies 12c and 12e to the first bus 427a. Likewise, for electrode bodies 12b and 12d to be initially coupled to the second terminal 140, so that electrode bodies 12b and 12d (like separate charging electrode 70) are anodes during charging, electrode body switches 425b and 425d may be controlled to connect electrode bodies 12b and 12d to the second bus 427b, where they are electrically connected to the second terminal 140 by charging electrode switch 170, which is closed during charging.
As charging progresses during the first phase 605 of the parallel charge mode 600, fuel growth may be bi-directional on the intermediate electrode bodies 12c and 12e that are acting as cathodes. In the embodiment of FIG. 16, metal fuel is initially growing on electrode body 12a towards electrode body 12b, due to the potential difference therebetween. Fuel is also growing on electrode body 12c both towards electrode body 12b and towards electrode body 12d Likewise, bidirectional fuel growth is occurring on electrode body 12e, towards both electrode body 12d and the separate charging electrode 70. During the charging, there may be, at 610, a number of continuity tests. Specifically, for N electrode bodies, there may be N−1 continuity tests performed to determine if an electrical connection has formed between any of the anodes and any of the cathodes. For example, at 610a, it may be determined if electrode body 12a has shorted to electrode body 12b Likewise, at 610b, it may be determined if an intermediate electrode body (i.e. electrode body 12c-d in the illustrated embodiment) has shorted with either of the electrode bodies adjacent to it. Additionally, at 610c, it may be determined if the last electrode body (i.e. the “N−1”th electrode, which is electrode body 12e in FIG. 16) has shorted with the separate charging electrode 70.
If any of the continuity tests at 610 indicate an electrical connection has formed between an anode and a cathode, the parallel charge mode 600 may progress to an iterative next phase at 615, wherein any shorted charging electrode (i.e. electrode body 12b or electrode body 12d) is electrically disconnected from the second terminal 140. For example, if any short occurs between the first bus 427a and the second bus 427b, whichever of the switches 425b-e that can be thrown to eliminate that electrical connection may be thrown accordingly.
In an embodiment, any of the intermediate electrode bodies 12b-e may be reassigned from acting as anodes to acting as cathodes, or vice versa, based on the electrical connections formed during the parallel charge mode 600. For example, if fuel growth electrically connects electrode body 12c (as a cathode) to electrode body 12d (as a charging electrode), while electrode body 12e is still growing fuel, the controller 230 may assign the pair of fuel-linked electrode bodies 12c-d to act together as a charging electrode, in that both electrode body switches 425c-d connect electrode bodies 12c-d to second terminal 140 via second bus 427b, so that bidirectional fuel growth of fuel on electrode body 12e continues. If fuel growth on electrode body 12a has electrically connected electrode bodies 12a-b, then electrode body 12b would be electrically disconnected from second bus 427b, such that a potential difference exists between electrode bodies 12a-b and electrode bodies 12c-d, so that additional fuel growth can occur on electrode bodies 12a-b (as a cathode) towards electrode bodies 12c-d (as a charging electrode).
If fuel growth on electrode body 12e, which is initially a cathode electrically connected to first terminal 130 via electrode body switch 425e and first bus 427a, causes a short with separate charging electrode 70, controller 230 may then throw electrode body switch 425e to electrically disconnect electrode body 425e from first bus 427a, such that electrode body 12e and the separate charging electrode 70, as well as the metal fuel therebetween, all act as an interconnected charging electrode. If electrode body 12d is then reassigned as a cathode (due to electrical connection with electrode body 12c, for example), then fuel growth may continue from electrode body 12d toward electrode body 12e, due to the potential difference therebetween.
In such a manner, the reassignment of electrode bodies 12b-d may progress, measured by the continuity tests at 610, until, at 620, either all electrode bodies 12a-e and the separate charging electrode 70 have shorted, or a threshold capacity for the cell 10 has been reached. Again, the reaching of the threshold capacity may be ascertained by any suitable mechanism, including in some embodiments taking measurements with the sensing device 236, or computing or estimating a charge capacity through controller 230. Regardless, once the threshold capacity has been reached, or all electrodes in the cell 10 have shorted, the cell may end the parallel charge mode 600 and enter an idle state, to await a future discharge mode.
In some embodiments, the controller 230 may be configured to charge the cell 10 such that some of the electrode bodies 12a-e are charging in accordance with progressive charge mode 500, while others of electrode bodies 12a-e are charging in accordance with parallel charge mode 600. In some embodiments, the varying desires of charge rate and energy density may be implemented in the charge mode selection at 440 throughout the charging of the cell 10, such that the real time needs of the application utilizing the cell 10 may be taken into account. In an embodiment the controller 230 may measure typical discharge characteristics of the cell 10 over time, and modify the selection of the charge mode at 440 accordingly. As one non-limiting example, if the cell 10 is utilized in an electric vehicle that is utilized intermittently during daylight hours, but is not utilized at night, then the controller 230 may utilize the parallel charge mode 600 to quickly charge the vehicle as needed during the daylight, however may utilize the progressive charge mode at night, so that the greater amount of stored energy is held by the cell 10 for use the following day. In an embodiment, the controller 230 may be more sophisticated, and may compute a more complex optimal energy vs. charge rate, to provide the optimal quantity of run time based on the usage of the cell 10.
It may be appreciated that in some embodiments the controller 230 may also be configured to discharge the cell 10 in a variety of modes. In some embodiments, the algorithm 430 may be further configured to select between a charging mode and a discharging mode. In other embodiments, a separate discharging algorithm may be provided for the discharge mode or modes. In some embodiments, differing modes of charging and discharging the cell 10 may be managed by a broader “cell operations” algorithm, which may be run on controller 230, for example. In some embodiments, only the oxidant electrode 14 and a distal electrode body (i.e. permeable electrode body 12a) are electrically connected to the load L, such that only the fuel electrically connects the permeable electrode bodies 12a-e. During discharge, the fuel would progressively be consumed from electrode body 12e (proximal to the oxidant electrode 14), towards the distal electrode body 12a. Once fuel is sufficiently consumed from each of the intermediate permeable electrode bodies 12b-d, those bodies would electrically disconnect from the fuel electrode 12 connected to the load L.
In some embodiments, the switching system 60 may be used to selectively connect the permeable electrode bodies 12b-e to the load L. In an embodiment, permeable electrode bodies 12b-e may all be connected to the load L throughout the discharging of the cell 10. In other embodiments, control of which electrode bodies (i.e. permeable electrode bodies 12b-e) are electrically connected to the load L may be ascertained by the discharging algorithm, and may depend on a particular discharge mode. In an embodiment, the determination to selectively connect or disconnect the permeable electrode bodies 12b-e from the load L may be based on measurements, manual overrides, or limits, which may be similar to those of determination criteria 450 that are used to determine the charge mode at 440 described above. For example, the decision to connect or disconnect one of the permeable electrode bodies may be based on criteria such as the voltage, current, slope of voltage, slope of current, charge capacity, or value of impedance or resistance. Such measurements in various embodiments may be taken over one or more of the electrode bodies 12a-12e, or across one or more cells 10. In an embodiment, sensors such as sensing device 236 associated with one or more of the electrode bodies 12a-e and/or one or more of the cells 10 may be utilized to take the measurements.
As above, in an embodiment the sensing device 236 may be, for example, a voltmeter (digital or analog), potentiometer, or other voltage measuring device or devices, which can be used to determine when to modify the configuration of the plurality of switches. In some embodiments, the sensing device 236 may instead measure current, resistance, or any other electrical or physical property across or of the cell 10 that may be used to determine when to modify the configuration of the plurality of switches. In some embodiments, the controller 230 may control the switches of the switching system 60 based on the passage of increments of time. For example, in an embodiment the time for fuel consumption between adjacent electrode bodies may be known, and used to calculate when to operate the switching system 60 so as to disconnect depleted ones of the electrode bodies 12b-e. 
The foregoing illustrated embodiments have been provided solely to illustrate the structural and functional principles of the present invention, and should not be regarded as limiting. To the contrary, the present invention is intended to encompass all modification, substitutions, and alterations within the spirit and scope of the following claims.
The subject matter claimed in the present application, owned by Fluidic, Inc., was developed as a result of activities undertaken within the scope of a license agreement qualifying as a joint research agreement under 35 U.S.C. §103(c)(2) and (3) between Fluidic, Inc. and Arizona Science and Technology Enterprises, LLC acting for the Board of Regents for and on behalf of Arizona State University, which was in effect prior to development of the claimed invention.

## Claims

1. An electrochemical cell comprising:
a fuel electrode comprising a series of permeable electrode bodies arranged in spaced apart relation;
an oxidant electrode spaced apart from the fuel electrode;
a charging electrode selected from the group consisting of (a) the oxidant electrode, (b) a third electrode spaced from the fuel electrode and the oxidant electrode, and (c) a portion of the fuel electrode;
an ionically conductive medium contacting the electrodes;
a controller coupled to a plurality of the electrode bodies of the fuel electrode, said controller being configured to apply an electrical current between the charging electrode and at least one of the permeable electrode bodies with the charging electrode functioning as an anode and the at least one permeable electrode body functioning as a cathode, such that reducible metal fuel ions in the ionically conductive medium are reduced and electrodeposited as metal fuel in oxidizable form on the at least one permeable electrode body, so that said electrodeposition causes growth of the metal fuel among the permeable electrode bodies with the electrodeposited metal fuel establishing an electrical connection between the permeable electrode bodies,
wherein said controller is configured to selectively apply the electrical current to a different number of said permeable electrode bodies, each functioning as a cathode, based on at least one input parameter so as to adjust a rate and density of the growth of the electrodeposited metal fuel.

2. An electrochemical cell according to claim 1, wherein said controller is configured to select between:
(1) a higher density progressive growth mode wherein the electrical current is applied to a terminal one of the permeable electrode bodies with the charging electrode functioning as the anode and the terminal electrode body functioning as the cathode such that the reducible metal fuel ions are reduced and electrodeposited as metal fuel in oxidizable form on the terminal permeable electrode body, said electrodeposition causing growth of the metal fuel among the permeable electrode bodies such that the electrodeposited metal fuel establishes an electrical connection between the terminal electrode body and each subsequent permeable electrode body with said reduction and deposition occurring on each subsequent permeable electrode body upon establishment of said electrical connection; and
(2) a higher rate growth mode wherein the electrical current is applied simultaneously to a plurality of said electrode bodies with the charging electrode functioning as the anode and each of the plurality of electrode bodies functioning as cathodes such that the reducible metal fuel ions are reduced and electrodeposited as metal fuel in oxidizable form on the terminal permeable electrode body, said electrodeposition causing growth of the metal fuel among the permeable electrode bodies.

3. An electrochemical cell according to claim 2, wherein the controller is configured to apply the electrical current in the higher rate growth mode simultaneously to all the electrode bodies.

4. An electrochemical cell according to claim 2, wherein the controller is configured to apply the electrical current in the higher rate growth mode simultaneously to less than all the electrode bodies.

5. An electrochemical cell according to claim 1, wherein said controller is configured to vary the number of electrode bodies to which the electrical current is applied while performing a recharging operation.

6. An electrochemical cell according to claim 1, wherein the controller is coupled to a sensor that senses a condition of the electrochemical cell, and wherein the input parameter is input by the sensor.

7. An electrochemical cell according to claim 1, wherein the input parameter is input via a user input.

8. An electrochemical cell according to claim 1, wherein the input parameter is a limit parameter and wherein the controller is further configured to compare a cell property to the limit parameter.

9. An electrochemical cell according to claim 8, wherein the cell property is a voltage, a capacity, an impedance between electrodes, a slope of electrode voltages, a current, a resistance to a sensing electrode, or a shorting to the charging electrode.

10. An electrochemical cell according to claim 1, wherein the ionically conductive medium is an electrolyte.

11. An electrochemical cell according to claim 1, further comprising a plurality of switches operatively coupled between the controller and the plurality of electrode bodies, wherein the controller is configured to control an open state and a closed state for each of the plurality of switches, to selectively apply the electrical current to some of the plurality of electrode bodies.

12. An electrochemical cell according to claim 2, wherein in the higher rate growth mode, the electrical current is applied simultaneously to the plurality of electrode bodies such that the charging electrode comprises some of the plurality of electrode bodies functioning as anodes and the fuel electrode comprises some of the plurality of electrode bodies functioning as cathodes, and wherein each of the plurality of electrode bodies functioning as cathodes are separated from one another by the plurality of electrode bodies functioning as anodes.

13. An electrochemical cell according to claim 1, wherein the controller is a charge/discharge controller.

14. An electrochemical cell according to claim 2, wherein the controller is a charge/discharge controller.

15. An electrochemical cell according to claim 6, wherein the controller is a charge/discharge controller.

16. An electrochemical cell according to claim 8, wherein the controller is a charge/discharge controller.

17. An electrochemical cell according to claim 12, wherein the controller is a charge/discharge controller.

18. A method of recharging an electrochemical cell, wherein the electrochemical cell comprises:
a fuel electrode comprising a series of permeable electrode bodies arranged in spaced apart relation;
an oxidant electrode spaced apart from the fuel electrode;
a charging electrode selected from the group consisting of (a) the oxidant electrode, (b) a third electrode spaced from the fuel electrode and the oxidant electrode, and (c) a portion of the fuel electrode;
an ionically conductive medium contacting the electrodes;
a controller coupled to a plurality of the electrode bodies of the fuel electrode, said controller being configured to apply an electrical current between the charging electrode and at least one of the permeable electrode bodies with the charging electrode functioning as an anode and the at least one permeable electrode body functioning as a cathode, such that reducible metal fuel ions in the ionically conductive medium are reduced and electrodeposited as metal fuel in oxidizable form on the at least one permeable electrode body, so that said electrodeposition causes growth of the metal fuel among the permeable electrode bodies with the electrodeposited metal fuel establishing an electrical connection between the permeable electrode bodies,
wherein said controller is configured to selectively apply the electrical current to a different number of said permeable electrode bodies based on at least one input parameter so as to adjust a rate and density of the growth of the electrodeposited metal fuel;
the method being performed using said electrochemical cell and comprising:
selecting, based on the at least one input parameter, between a higher density progressive growth mode and a higher rate growth mode;
charging the electrochemical cell based on the selected one of the higher density progressive charge mode and the higher rate growth mode;
wherein, in the higher density progressive growth mode, said charging comprises:
applying the electrical current to a terminal one of the permeable electrode bodies, with the charging electrode functioning as the anode and the terminal electrode body functioning as the cathode, such that the reducible metal fuel ions are reduced and electrodeposited as metal fuel in oxidizable form on the terminal permeable electrode body, said electrodeposition causing growth of the metal fuel among the permeable electrode bodies such that the electrodeposited metal fuel establishes an electrical connection between the terminal electrode body and each subsequent permeable electrode body with said reduction and deposition occurring on each subsequent permeable electrode body upon establishment of said electrical connection; and

wherein, in the higher rate growth mode, said charging comprises:
applying the electrical current simultaneously to a plurality of said electrode bodies, with the charging electrode functioning as the anode and each of the plurality of electrode bodies functioning as cathodes, such that the reducible metal fuel ions are reduced and electrodeposited as metal fuel in oxidizable form on the terminal permeable electrode body, said electrodeposition causing growth of the metal fuel among the permeable electrode bodies; and

disconnecting the electrical current to discontinue the charging.

19. A method of recharging the electrochemical cell according to claim 18, wherein, in the higher rate growth mode, the charging electrode comprises one or more of the plurality of electrode bodies adjacent to the plurality of the electrode bodies functioning as cathodes.

20. A method of recharging the electrochemical cell according to claim 18, wherein, in the higher rate growth mode, said charging further comprises performing continuity testing on one or more of the plurality of electrode bodies to determine electrical connections formed between any of the electrode bodies functioning as cathodes and any of the charging electrode; and disconnecting any of the electrode bodies.

21. A method of recharging the electrochemical cell according to claim 18, wherein the at least one input parameter comprises measurements obtained by a sensor associated with the electrochemical cell, and wherein the method further comprises sensing, with the sensor, the measurements of the electrochemical cell.

22. A method of recharging the electrochemical cell according to claim 18, wherein the at least one input parameter comprises a user selection of the higher density progressive charge mode or the higher rate growth mode, input via a user input, wherein the method further comprises receiving a user selection via the user input.

23. A method of recharging the electrochemical cell according to claim 18, wherein the at least one input parameter is a limit parameter and wherein the controller is further configured to compare a cell property to the limit parameter to perform said selecting.

24. A method of recharging the electrochemical cell according to claim 18, wherein, in the higher rate growth mode, said charging comprises applying the electrical current simultaneously to all of the electrode bodies.

25. A method of recharging the electrochemical cell according to claim 18, wherein, in the higher rate growth mode, said charging comprises applying the electrical current simultaneously to less than all of the electrode bodies.

26. A method of recharging the electrochemical cell according to claim 18, wherein said charging comprises varying, with the controller, the number of electrode bodies to which the electrical current is applied while performing a recharging operation.

27. A method of recharging the electrochemical cell according to claim 18, wherein the ionically conductive medium of the electrochemical cell is an electrolyte.

28. A method of recharging the electrochemical cell according to claim 18, wherein the electrochemical cell further comprises a plurality of switches operatively coupled between the controller and the plurality of electrode bodies, and wherein said charging comprises controlling an open state and a closed state for each of the plurality of switches with the controller, to selectively apply the electrical current to some of the plurality of electrode bodies.

29. A method of recharging the electrochemical cell according to claim 18, wherein in the higher rate growth mode, said charging comprises applying the electrical current simultaneously to the plurality of electrode bodies such that the charging electrode comprises some of the plurality of electrode bodies functioning as anodes and the fuel electrode comprises some of the plurality of electrode bodies functioning as cathodes, and wherein each of the plurality of electrode bodies functioning as cathodes are separated from one another by the plurality of electrode bodies functioning as anodes.

30. A method according to claim 18, wherein the controller is a charge/discharge controller.

31. A method according to claim 21, wherein the controller is a charge/discharge controller.

32. A method according to claim 23, wherein the controller is a charge/discharge controller.

33. A method according to claim 28, wherein the controller is a charge/discharge controller.