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.

1 . A method of charging a flow battery, comprising:
 providing a uniform high current density across a low resistance positive electrode and a low resistance negative electrode, the high current density passing through a deposition region of a deposition surface of a negative half-cell of the flow battery;   generating a super-saturated electrolyte flow through a flow channel of the negative half cell with a high rate of mixing in a deposition region proximate the deposition surface, wherein the super-saturated electrolyte has a zinc ion concentration greater than 0.4N; and   maintaining a mass transfer coefficient of the flow proximate the deposition surface sufficiently large to maintain a sufficient electrolyte concentration proximate the deposition surface for substantially uniform deposition in the region of the deposition surface.   
     
     
         2 . The method of  claim 1 , wherein the super-saturated electrolyte has a sufficient concentration of zinc ions for deposition rates on the deposition surface that sustains the uniform high current density through the deposition surface during the charging. 
     
     
         3 . The method of  claim 1 , wherein the super-saturated electrolyte has a zinc solubility of greater than about 0.7M in a 4N NaOH containing solution. 
     
     
         4 . The method of  claim 1 , wherein the super-saturated electrolyte has a zinc solubility of about 0.73M in a 4N NaOH containing solution. 
     
     
         5 . The method of  claim 1 , wherein the super-saturated electrolyte is prepared by combining zinc oxide (ZnO) with NaOH pellets. 
     
     
         6 . The method of  claim 1 , wherein the uniform high current density is greater than 70 mA/cm2. 
     
     
         7 . The method of  claim 1 , wherein a mass transfer coefficient of the super-saturated electrolyte has a value in the approximate range of 5.3×10−4 m/s to 12.4×10−3 m/s. 
     
     
         8 . The method of  claim 1 , wherein the flow battery is a flow battery selected from the group consisting of: a ZnFe flow battery, a ZnHBr flow battery, a ZnBr flow battery, a CeZn flow battery; and a ZnCl flow battery. 
     
     
         9 . The method of  claim 1 , wherein the flow channel is configured to provide a high rate of mixing of the super-saturated electrolyte in the negative plating zone proximate the surface of the negative electrode.