High performance flow battery

Abstract

High performance flow batteries, based on alkaline zinc/ferro-ferricyanide rechargeable (“ZnFe”) and similar flow batteries, may include one or more of the following improvements. First, the battery design has a cell stack comprising a low resistance positive electrode in at least one positive half cell and a low resistance negative electrode in at least one negative half cell, where the positive electrode and negative electrode resistances are selected for uniform high current density across a region of the cell stack. Second, a flow of electrolyte, such as zinc species in the ZnFe battery, with a high level of mixing through at least one negative half cell in a Zn deposition region proximate a deposition surface where the electrolyte close to the deposition surface has sufficiently high zinc concentration for deposition rates on the deposition surface that sustain the uniform high current density. The mixing in the flow may be induced by structures such as: conductive and non-conductive meshes; screens; ribbons; foam structures; arrays of cones, cylinders, or pyramids; and other arrangements of wires or tubes used solely or in combination with a planar electrode surface. Third, the zinc electrolyte has a high concentration and in some embodiments has a concentration greater than the equilibrium saturation concentration—the zinc electrolyte is super-saturated with Zn ions.

1 . A flow battery comprising:
 at least one cell comprising a low resistance positive electrode in a positive half cell and a low resistance negative electrode in a negative half cell; and   a pump for circulating electrolyte through a flow channel of said negative half cell, wherein said pump and said channel are configured to provide a high rate of mixing of said electrolyte in a deposition region proximate a deposition surface;   wherein said electrolyte has a metal ion concentration greater than the equilibrium saturation concentration of the metal ion in said electrolyte.   
     
     
         2 . The flow battery of  claim 1 , wherein the resistance across a cell results in less than 200 mV loss at an operating current density of 100 mA/cm 2 . 
     
     
         3 . The flow battery of  claim 1 , wherein a mass transfer coefficient of said electrolyte in said deposition region is sufficient to maintain an electrolyte concentration of metal ions proximate said deposition surface for a substantially uniform deposition of metal on said deposition surface. 
     
     
         4 . The flow battery of  claim 3 , wherein said mass transfer coefficient is greater than approximately 2×10 −4  m/s. 
     
     
         5 . The flow battery of  claim 1 , wherein said electrolyte has sufficiently high metal ion concentration for deposition rates on said deposition surface that sustain said uniform high current density during a charging cycle. 
     
     
         6 . The flow battery of  claim 1 , wherein said electrolyte has a zinc solubility of greater than 0.37M in 4N NaOH. 
     
     
         7 . The flow battery of  claim 1 , wherein said electrolyte has a zinc solubility of greater than 0.7M in 4N NaOH. 
     
     
         8 . The flow battery of  claim 1 , wherein the flow of said electrolyte through said flow channel is turbulent. 
     
     
         9 . The flow battery of  claim 1 , wherein a Reynolds Number of said flow channel is greater than approximately 1300. 
     
     
         10 . The flow battery of  claim 1 , wherein a Sherwood Number of said flow channel is greater than approximately 21. 
     
     
         11 . The flow battery of  claim 1 , wherein said uniform high current density is greater than 100 mA/cm 2 . 
     
     
         12 . The flow battery of  claim 1 , further comprising at least one mixing element in said flow channel. 
     
     
         13 . The flow battery of  claim 12 , wherein said mixing element induces turbulence in said flow channel. 
     
     
         14 . The flow battery of  claim 12 , wherein said mixing element is chosen from the group consisting of wires, arrays of cones, arrays of pyramids, foam, mesh, and tubes. 
     
     
         15 . The flow battery of  claim 1 , further comprising a flow calming structure positioned in said electrolyte circuit after said flow channel of said negative half cell. 
     
     
         16 . The flow battery of  claim 1 , wherein said flow battery is a ZnFe flow battery. 
     
     
         17 . A method of charging a flow battery comprising, circulating electrolyte through a flow channel of a negative half cell in said flow battery, wherein said flow channel is configured to provide a high rate of mixing of said electrolyte in a metal deposition region proximate a deposition surface of said negative half cell. 
     
     
         18 . The method of  claim 17 , wherein said circulating includes pumping said electrolyte through a fluid circuit, said fluid circuit including said flow channel. 
     
     
         19 . The method of  claim 17 , wherein said electrolyte has a metal ion concentration greater than the equilibrium saturation concentration of said metal ion in said electrolyte. 
     
     
         20 . The method of  claim 17 , further comprising providing a uniform high current density across a low resistance positive electrode and a low resistance negative electrode of said flow battery, said high current density passing through said metal deposition region proximate said deposition surface of said negative half cell. 
     
     
         21 . The method of  claim 17 , wherein a mass transfer coefficient of said electrolyte proximate said deposition surface has a value in the approximate range of 5.3×10 −4  m/s to 12.4×10 −3  m/s. 
     
     
         22 . A ZnFe flow battery comprising:
 at least one cell comprising a low resistance positive electrode in a positive half cell and a low resistance negative electrode in a negative half cell;   a pump for circulating electrolyte through a flow channel of said negative half cell, wherein said pump and said channel are configured to provide a high rate of mixing of said electrolyte in a deposition region proximate a deposition surface;   wherein said electrolyte has a zinc metal ion concentration greater than the equilibrium saturation concentration of said zinc metal ion in said electrolyte, and wherein a mass transfer coefficient of said electrolyte in said deposition region is sufficient to maintain an electrolyte concentration of zinc metal ions proximate said deposition surface for a substantially uniform deposition of zinc metal on said deposition surface at a uniform high current density.   
     
     
         23 . The flow battery of  claim 22 , wherein said uniform high current density is greater than 70 mA/cm 2 .