Metal-air electrochemical cell with high energy efficiency mode

Abstract

The present invention relates to a metal-air electrochemical cell with a high energy efficiency mode.

What is claimed: 
     
         1 . A metal-air electrochemical cell for storing electrical energy from a power source and supplying electrical energy to a load, comprising:
 a plurality of electrodes comprising a fuel electrode comprising a metal fuel and an air electrode for exposure to an oxygen source, wherein an electrode of the plurality other than the fuel electrode comprises a reversible metal capable of reversible oxidation to a reducible species thereof and reduction to an oxidizable species thereof, and wherein an electrode of the plurality other than the fuel electrode has an oxygen evolving functionality;   an ionically conductive medium for conducting ions among the plurality of electrodes;   a controller configured to operate the cell in the following states:   (i) a standard recharge state wherein the power source is coupled to the fuel electrode and the oxygen evolving electrode for applying a potential difference therebetween to cause reduction of a reducible species of the metal fuel on the fuel electrode and evolution of oxygen from the ionically conductive medium at the oxygen evolving electrode;   (ii) a standard discharge state wherein the fuel electrode and the air electrode are coupled to the load such that oxidation of the metal fuel at the fuel electrode and reduction of oxygen from the oxygen source at the air electrode generates a potential difference for outputting current;   (iii) a high energy efficiency recharge state wherein the power source is coupled to the fuel electrode and the electrode comprising the reversible metal for applying a potential difference therebetween to cause reduction of a reducible species of the metal fuel on the fuel electrode and oxidizing the oxidizable species of the reversible metal, if present, to the reducible species thereof with the potential of the electrode comprising the reversible metal being cathodic of the potential for oxygen evolution; and   (iv) a high energy efficiency discharge state wherein the fuel electrode and the electrode comprising the reversible metal are coupled to the load such that oxidation of the metal fuel at the fuel electrode and reduction of the reducible species of the reversible metal, if present, to the oxidizable species thereof generates a potential difference for outputting current with the potential of the electrode reversible metal being anodic of the potential for oxygen reduction at the air electrode;   wherein an energy efficiency of the high energy efficiency discharge and recharge states is greater than an energy efficiency of the standard discharge and recharge states, each energy efficiency being the ratio of q out V out /q in V in .   wherein the air electrode, the electrode comprising the reversible metal and the oxygen evolving electrode are the same electrode which is a quad-functional electrode, such that the load is coupled to the fuel electrode and the quad-functional electrode in both the standard and high efficiency discharge states and the power source is coupled to the fuel electrode and the quad-functional electrode in both the standard and high efficiency recharge states; and   wherein the controller includes a regulator coupled to at least the quad-functional electrode to control the potential at the quad-functional electrode for setting its potential anodic of the potential for oxygen reduction during the high efficiency discharge state and cathodic of the potential for oxygen evolution during the high efficiency recharge state.   
     
     
         2 . A metal-air electrochemical cell according to  claim 1 , wherein the reversible metal is a nickel species. 
     
     
         3 . A metal-air electrochemical cell according to  claim 2 , wherein the oxidizable species of the nickel is Ni(OH) 2  and the reducible species of the nickel is NiOOH. 
     
     
         4 . A metal-air electrochemical cell according to  claim 1 , wherein said controller is configured to switch between the states thereof based on predetermined criteria. 
     
     
         5 . A metal-air electrochemical cell according to  claim 1 , wherein the fuel is selected from the group consisting of an alkaline earth metal, a transition metal, and a post-transition metal. 
     
     
         6 . A metal-air electrochemical cell according to  claim 1 , wherein the fuel is selected from the group consisting of zinc, aluminum, magnesium, manganese, and iron. 
     
     
         7 . A metal-air electrochemical cell according to  claim 2 , wherein the fuel is selected from the group consisting of an alkaline earth metal, a transition metal, and a post-transition metal. 
     
     
         8 . A metal-air electrochemical cell according to  claim 2 , wherein the fuel is selected from the group consisting of zinc, aluminum, magnesium, manganese, and iron. 
     
     
         9 . A metal-air electrochemical cell according to  claim 3 , wherein the fuel is selected from the group consisting of an alkaline earth metal, a transition metal, and a post-transition metal. 
     
     
         10 . A metal-air electrochemical cell according to  claim 3 , wherein the fuel is selected from the group consisting of zinc, aluminum, magnesium, manganese, and iron. 
     
     
         11 . A metal-air electrochemical cell according to  claim 1 , wherein the ionically conductive medium is an alkaline aqueous electrolyte solution. 
     
     
         12 . A metal-air electrochemical cell according to  claim 2 , wherein the ionically conductive medium is an alkaline aqueous electrolyte solution. 
     
     
         13 . A metal-air electrochemical cell according to  claim 3 , wherein the ionically conductive medium is an alkaline aqueous electrolyte solution. 
     
     
         14 . A metal-air electrochemical cell according to  claim 7 , wherein the ionically conductive medium is an alkaline aqueous electrolyte solution. 
     
     
         15 . A metal-air electrochemical cell according to  claim 8 , wherein the ionically conductive medium is an alkaline aqueous electrolyte solution. 
     
     
         16 . A method for operating an electrochemical cell for storing energy from a power source and supplying energy to a load, the cell comprising a plurality of electrodes comprising a fuel electrode comprising a metal fuel and an air electrode, wherein an electrode of the plurality other than the fuel electrode comprises a reversible metal capable of reversible oxidation to a reducible species thereof and reduction to an oxidizable species thereof, and wherein an electrode of the plurality other than the fuel electrode has an oxygen evolving functionality; the method comprising:
 operating the cell in the following states:   (i) a standard recharge state wherein the power source is coupled to the fuel electrode and the oxygen evolving electrode for applying a potential difference therebetween to cause reduction of a reducible species of the metal fuel on the fuel electrode and evolution of oxygen from the ionically conductive medium at the oxygen evolving electrode;   (ii) a standard discharge state wherein the fuel electrode and the air electrode are coupled to the load such that oxidation of the metal fuel at the fuel electrode and reduction of oxygen from the oxygen source at the air electrode generates a potential difference for outputting current;   (iii) a high energy efficiency recharge state wherein the power source is coupled to the fuel electrode and the electrode comprising the reversible metal for applying a potential difference therebetween to cause reduction of a reducible species of the metal fuel on the fuel electrode and oxidizing the oxidizable species of the reversible metal, if present, to the reducible species thereof with the potential of the electrode comprising the reversible metal being cathodic of the potential for oxygen evolution; and   (iv) a high energy efficiency discharge state wherein the fuel electrode and the electrode comprising the reversible metal are coupled to the load such that oxidation of the metal fuel at the fuel electrode and reduction of the reducible species of the reversible metal, if present, to the oxidizable species thereof generates a potential difference for outputting current with the potential of the electrode reversible metal being anodic of the potential for oxygen reduction at the air electrode;   wherein an energy efficiency of the high energy efficiency discharge and recharge states is greater than an energy efficiency of the standard discharge and recharge states, each energy efficiency being the ratio of q out V out /q in V in .   
     
     
         17 . A method according to  claim 16 , wherein the electrode comprising the reversible metal and the oxygen evolving electrode are the same electrode which is a tri-functional electrode separate from both the fuel electrode and the air electrode; and
 wherein operating the cell in the standard and high efficiency recharge states comprises operating the cell in a recharge state coupling the power source to the fuel electrode and the tri-functional electrode such that the recharge state includes (a) initially the high energy recharge state in which oxidation at the tri-functional electrode is predominated by oxidation of the oxidizable species of the reversible metal, if present, to the reducible species thereof with the potential of the tri-functional electrode being cathodic of the potential for oxygen evolution, and (b) then the standard recharge state in which the oxidation at the tri-functional electrode is predominated by evolution of oxygen from the ionically conductive medium.   
     
     
         18 . A method according to  claim 16 , wherein the electrode comprising the reversible metal and the oxygen evolving electrode are separate electrodes and are each separate from both the fuel electrode and the air electrode. 
     
     
         19 . A method according to  claim 16 , wherein the air electrode, the electrode comprising the reversible metal and the oxygen evolving electrode are the same electrode which is a quad-functional electrode, such that the load is coupled to the fuel electrode and the quad-functional electrode in both the standard and high efficiency discharge states and the power source is coupled to the fuel electrode and the quad-functional electrode in both the standard and high efficiency recharge states; and
 wherein a regulator is coupled to at least the quad-functional electrode to control the potential at the quad-functional electrode for setting its potential anodic of the potential for oxygen reduction during the high efficiency discharge state and cathodic of the potential for oxygen evolution during the high efficiency recharge state.   
     
     
         20 . A method according to  claim 16 , wherein the reversible metal is a nickel species. 
     
     
         21 . A method according to  claim 20 , wherein the oxidizable species of the nickel is Ni(OH) 2  and the reducible species of the nickel is NiOOH. 
     
     
         22 . A method according to  claim 16 , wherein the fuel is selected from the group consisting of an alkaline earth metal, a transition metal, and a post-transition metal. 
     
     
         23 . A method according to  claim 16 , wherein the fuel is selected from the group consisting of zinc, aluminum, magnesium, manganese, and iron. 
     
     
         24 . A method according to  claim 16 , wherein the ionically conductive medium is an alkaline aqueous electrolyte solution.