IN-SITU ELECTROLYTE PREPARATION IN FLOW BATTERY

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.