Methods for determining state of charge and calibrating reference electrodes in a redox flow battery

Patent metadata

Field	Value
Publication number	US-10388978-B2
Application number	US-201415027228-A
Country	US
Kind code	B2
Filing date	Nov 6, 2014
Priority date	Nov 15, 2013
Publication date	Aug 20, 2019
Grant date	Aug 20, 2019

Abstract

The invention concerns methods of determining the state of charge of a half-cell within a redox flow battery, the method comprising: (i) measuring the rate of change in equilibrium half-cell reduction potential of the electrolyte as charge is passed into the electrolyte solution within the cell; and (ii) correlating said rate of change in equilibrium half-cell reduction potential with the state of charge of said half-cell. Other aspects of the invention concern balancing the state of charge of a flow battery and methods of calibrating an oxidation/reduction probe.

First claim

What is claimed:

1. A method of determining the state of charge of an electrolyte within an operating half-cell within a redox flow battery wherein the electrolyte exhibits an instantaneous equilibrium half-cell reduction potential at any given point in time, said method comprising:
measuring the instantaneous equilibrium half-cell reduction potential of the electrolyte as a function of charge that has passed into an electrolyte solution within the half-cell during operation of the operating redox flow battery; wherein the change in the instantaneous equilibrium half-cell reduction potential as a function of charge that has passed through the electrolyte solution is reflective of the state of charge of the electrolyte, which can be determined by solving the equation

dE
dS

=

-

RT

n
⁢

⁢
F

⁢

(

100

S
2

-

100
⁢
S

)

where,
E is the equilibrium half-cell reduction potential,
S is the percent of an electrolyte species in a reduced state,
T is the temperature of the electrolyte,
R is the gas constant,
n is the number of electrons in the reaction,
F is Faraday's constant,
dE is the differential change in equilibrium half-cell reduction potential,
dS is the differential change in the percent of a reduced electrolyte species and is determined by the equation

dS
=

A
·
h

c
·
V
·
F
·

1
3600

,

where,
A is the amount of current passed through the electrolyte solution,
h is the number of hours the current was passed into the electrolyte solution,
c is the concentration of an active material in the electrolyte solution,
V is the volume of the electrolyte solution, and
F is Faraday's constant.

2. The method of claim 1 , wherein said equilibrium half-cell reduction potential is measured using a carbon electrode and a Ag/AgCl reference electrode.

3. The method of claim 2 , wherein said carbon electrode is a glassy carbon electrode.

4. The method of claim 1 , wherein correlating said rate of change is made utilizing a set of calibration data, the set of calibration data relating at least one state of charge to at least one rate of change in equilibrium half-cell reduction potential.

5. The method of claim 1 , wherein a relationship between said rate of change in equilibrium half-cell reduction potential and the state of charge of said half-cell follows the Nernst equation.

6. The method of claim 1 , wherein a relationship between said rate of change in equilibrium half-cell reduction potential and the state of charge of said half-cell does not follow the Nernst equation.

7. The method of claim 1 , wherein said half-cell is either half-cell-in a flow battery comprising:
a first half-cell comprising a first aqueous electrolyte comprising a first redox active material, and a first electrode in contact with said first aqueous electrolyte;
a second half-cell comprising a second aqueous electrolyte comprising a second redox active material, and a second electrode in contact with said second aqueous electrolyte; and
a separator comprising a membrane disposed between said first and second aqueous electrolytes; and
wherein said first and second electrodes are not the same electrodes as those used for measuring the rate of change in equilibrium half-cell reduction potential of the electrolyte as charge is passed into the electrolyte solution within the first or second half-cell.

8. The method of claim 7 , wherein said membrane is an ionomer membrane.

9. A method of balancing the state of charge between two half-cells of a redox flow battery, said method comprising:
determining the state of charge of a first half-cell within said redox flow battery, said first half-cell comprising a first electrolyte solution, said determination being made by measuring a first rate of change in equilibrium half-cell reduction potential of said first half-cell as current is passed through said first electrolyte solution, and correlating said first rate of change in equilibrium half-cell reduction potential with the state of charge of said first half-cell;
determining the state of charge of a second half-cell within said redox flow battery, said second half-cell comprising a second electrolyte solution, said determination being made by measuring a second rate of change in equilibrium half-cell reduction potential of said second half-cell as current is passed through said second electrolyte solution, and correlating said second rate of change in equilibrium half-cell reduction potential with the state of charge of said second half-cell;
determining a difference between the states of charge of the first and second half-cells; and
if the difference in state of charge between said first and second half-cells exceeds a first predetermined value, recharging at least one half-cell such that the difference in state of charge between said first and second half-cells is less than a second predetermined value; wherein said first predetermined value is greater than said second predetermined value.

10. The method of claim 9 , wherein the rate of change in equilibrium half-cell reduction potential (dE/dS) is determined by the equation

dE
dS

=

-

RT

n
⁢

⁢
F

⁢

(

100

S
2

-

100
⁢
S

)

Assignees

• Lockheed Martin Energy Llc

Inventors

• Morris-Cohen Adam
• Duffey Kean
• Hays Peter F
• Lee Sophia

Classifications

• H02J7/865

  Battery or charger load switching, e.g. concurrent charging and load supply (H02J7/50 takes precedence) · CPC title

• H01M8/04544

  Voltage · CPC title

• H01M8/04604

  Power, energy, capacity or load · CPC title

• G01N27/4168

  Oxidation-reduction potential, e.g. for chlorination of water (water analysis G01N33/18) · CPC title

• H01M8/188 Primary

  by recharging of redox couples containing fluids; Redox flow type batteries · CPC title