In-situ electrolyte preparation in flow battery

Abstract

A method of in-situ electrolyte preparation in a flow battery includes providing a vanadium-based electrolyte solution having vanadium ions of predominantly vanadium V 4+ to a first electrode and a second electrode of at least one cell of a flow battery. The vanadium V 4+ at the first electrode is converted to vanadium V 3+ and the vanadium V 4+ at the second electrode is converted to vanadium V 5+ by providing electrical energy to the electrodes. A reducing agent is then provided to the vanadium V 5+ at the second electrode to reduce the V 5+ to vanadium the V 4+ . The vanadium V 3+ at the first electrode is then converted to vanadium V 2+ and the vanadium V 4+ at the second electrode is then converted to vanadium V 5+ by providing electrical energy to the electrodes. A simple method to produce predominantly vanadium V 4+ electrolyte from a V 5+ source, such as V 2 O 5 , is also taught.

What is claimed is: 
     
         1 . A method of in-situ electrolyte preparation in a flow battery, the method comprising:
 (a) providing a vanadium-based electrolyte solution having vanadium ions of predominantly vanadium V 4+  to a first electrode and a second electrode of at least one cell of a flow battery, the second electrode being spaced apart from the first electrode, with an electrolyte separator layer arranged between the first electrode and the second electrode;   (b) converting the vanadium V 4+  in the vanadium-based electrolyte solution at the first electrode to vanadium V 3+  and converting the vanadium V 4+  in the vanadium-based electrolyte solution at the second electrode to vanadium V 5+  by providing electrical energy through an electric circuit to the first electrode and the second electrode;   (c) after said step (b), providing a reducing agent to the vanadium-based electrolyte solution of the second electrolyte to reduce the vanadium V 5+  to vanadium V 4+ ; and   (d) after said step (c), converting the vanadium V 3+  of said step (b) in the vanadium-based electrolyte solution at the first electrode to vanadium V 2+  and converting the vanadium V 4+  of said step (c) in the vanadium-based electrolyte solution at the second electrode to vanadium V 5+  by providing electrical energy through the electric circuit to the first electrode and the second electrode.   
     
     
         2 . The method as recited in  claim 1 , wherein the reducing agent includes an acid. 
     
     
         3 . The method as recited in  claim 1 , wherein the reducing agent includes oxalic acid. 
     
     
         4 . The method as recited in  claim 1 , wherein the reducing agent includes formic acid. 
     
     
         5 . The method as recited in  claim 1 , wherein the reducing agent includes an alcohol. 
     
     
         6 . The method as recited in  claim 1 , wherein the vanadium ions of said step (a) have a concentration of 90% or greater of the vanadium V 4+ . 
     
     
         7 . The method as recited in  claim 1 , wherein the vanadium ions of said step (a) have a concentration of 95% or greater of vanadium V 4+ . 
     
     
         8 . The method as recited in  claim 1 , wherein the vanadium-based electrolyte solution includes sulfuric acid. 
     
     
         9 . The method as recited in  claim 1 , wherein equal parts of the vanadium-based electrolyte solution in said step (a) are provided to the first electrode and the second electrode. 
     
     
         10 . The method as recited in  claim 9 , wherein the concentration of the vanadium V 2+  of said step (d) in the vanadium-based electrolyte solution at the first electrode is equal to the concentration of the vanadium V 5+  of said step (d) in the vanadium-based electrolyte solution at the second electrode within +/−5%. 
     
     
         11 . The method as recited in  claim 1 , further comprising preparing the vanadium-based electrolyte solution having vanadium ions of predominantly vanadium V 4+  of said step (a) by:
 (i) providing a first solution and a second solution, at least one of the first solution and the second solution including vanadium V 5+ , at least one of the first solution and the second solution including a reducing agent, and a ratio of moles of the reducing agent to moles of vanadium V 5+  is 2:1 or greater; and 
 (ii) combining the first solution and the second solution, the reducing agent reducing the vanadium V 5+  to the vanadium V 4+ . 
 
     
     
         12 . A method of preparing a vanadium-based electrolyte solution having vanadium ions of predominantly V 4+ , the method comprising:
 (a) providing a first solution and a second solution, at least one of the first solution and the second solution including vanadium V 5+ , at least one of the first solution and the second solution including a reducing agent, and a ratio of moles of the reducing agent to moles of vanadium V 5+  is 2:1 or greater; and   (b) combining the first solution and the second solution, the reducing agent reducing the vanadium V 5+  to vanadium V 4+ .   
     
     
         13 . The method as recited in  claim 12 , wherein the first solution includes the reducing agent and the second solution includes an acid. 
     
     
         14 . The method as recited in  claim 13 , wherein the reducing agent includes oxalic acid and the acid of the second solution includes sulfuric acid. 
     
     
         15 . The method as recited in  claim 13 , wherein the reducing agent includes formic acid and the acid of the second solution includes sulfuric acid. 
     
     
         16 . The method as recited in  claim 13 , wherein the reducing agent includes an alcohol and the acid of the second solution includes sulfuric acid. 
     
     
         17 . The method as recited in  claim 12 , wherein the first solution of said step (a) includes the reducing agent and the vanadium V 5+ . 
     
     
         18 . The method as recited in  claim 12 , further comprising providing the at least one of the first solution and the second solution including vanadium V 5+  using V 2 O 5  powder. 
     
     
         19 . A flow battery comprising:
 at least one cell including a first electrode, a second electrode spaced apart from the first electrode and an electrolyte separator layer arranged between the first electrode and the second electrode;   a supply/storage system external of the at least one cell, the supply/storage system including first and second vessels fluidly connected with the at least one cell; and   first and second fluid electrolytes in, respectively, the first and second vessels, each of the first and second fluid electrolytes having vanadium ions of predominantly vanadium V 4+ , the first and second fluid electrolytes having substantially equivalent amounts of vanadium ions of predominantly vanadium V 4+ .   
     
     
         20 . The flow battery as recited in  claim 19 , wherein the battery is initially charged to a fully charged state by two separate electrochemical charging steps with the addition of a reducing fluid to one of the electrolytes in between the two charging steps.