Apparatus and Methods of Determination of State of Charge in a Redox Flow Battery

• US 20080193828A1
• Filed: 02/12/2007
• Published: 08/14/2008
• Est. Priority Date: 02/12/2007
• Status: Active Grant

• Current Assignee: Imergy Power Systems, Inc.
• Original Assignee: Deeya Energy Incorporated
• Inventors: Sahu, Saroj Kumar
• Granted Patent: US 7,855,005 B2
• Time in Patent Office: Days
• US Class Current: 429/63
• CPC Class Codes: B60L 50/64 Constructional details of batteries specially adapted for electric vehicles
• CPC Class Codes: B60L 53/80 Exchanging energy storage elements, e.g. removable batteries
• CPC Class Codes: G01N 21/05 Flow-through cuvettes G01N21/09 takes precedence; handling fluid samples G01N1/10
• CPC Class Codes: G01N 21/80 Indicating pH value
• CPC Class Codes: H01M 10/42 Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells H01M10/60 takes precedence
• CPC Class Codes: H01M 8/04186 of liquid-charged or electrolyte-charged reactants
• CPC Class Codes: H01M 8/188 by recharging of redox couples containing fluids; Redox flow type batteries
• CPC Class Codes: Y02E 60/10 Energy storage using batteries
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 90/12 Electric charging stations
• CPC Class Codes: Y02T 90/14 Plug-in electric vehicles

Abstract

Apparatus and methods for determining the individual states of charge of electrolytes in a redox battery with mixed or unmixed reactants by optical absorption spectrophotometry are disclosed. The state of charge thus obtained may serve as a gauge for the amount of electro-chemical energy left in the system. Further, the information on anolyte and catholyte charge states may be used for any rebalancing mechanism if the states are different.

Claims

1. A redox flow battery comprising:

an anolyte having different optical absorption spectra in reduced and oxidized forms;

a catholyte having different optical absorption spectra in reduced and oxidized forms; and

a spectrophotometer for independently measuring the optical absorption spectra of said anolyte and said catholyte.

2. The redox flow battery of claim 1, wherein said anolyte and said catholyte comprise acidic solutions.

3. The redox flow battery of claim 1, wherein said acidic solutions comprise hydrochloric acid, hydrobromic acid or a mixture thereof.

4. The redox flow battery of claim 1, wherein said acidic solutions further comprise aqueous metal chloride salts.

8. The redox flow battery of claim 1, wherein

said anolyte comprises an acidic solution comprising

Cr²⁺ and Fe²⁺ in the completely charged state;

Cr³⁺ and Fe²⁺ in the completely discharged state;

said catholyte comprises an acidic solution comprising

Cr³⁺ and Fe³⁺ in the completely charged state; and

Cr³⁺ and Fe²⁺ in the completely discharged state.

11. The redox flow battery of claim 1, wherein said spectrophotometer comprises at least one light emitter and at least one light receiver.

13. The redox flow battery of claim 11, comprising two light emitters, wherein

one light emitter is for anolyte photometry;

and

one light emitter is for catholyte photometry.

15. The redox flow battery of claim 11, wherein said light emitters emit light as photometric beams with spectral bandwidths less than about 50 nm at FWHM (Full Width at Half Maximum).

18. The redox flow battery of claim 15, further comprising at least one transparent tube, wherein said tube intercepts at least one of said photometric beams.

19. The redox flow battery of claim 18, wherein at least one electrolyte flows through said transparent tube.

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43. An electrolyte rebalancing, electrical energy storage system comprising:

a redox flow battery comprising a first electrolyte that exhibits a first optical absorption spectra and a second electrolyte that exhibits a second optical absorption spectra;

a spectrophotometer for measuring said first and second optical absorption spectra of said first and second electrolyte respectively;

a means for correlating said first and second optical absorption spectra with the state of charge of said first and second electrolyte respectively; and

a rebalance mechanism for restoring charge balance when a charge imbalance is detected as between said first and second electrolytes as determined by their respective optical absorption spectra.

44. The energy storage system claim 43, wherein said electrolytes comprise acidic solutions.

45. The redox flow battery of claim 44, wherein said acidic solutions comprise hydrochloric acid, hydrobromic acid or a mixture thereof.

46. The redox flow battery of claim 44, wherein said acidic solutions further comprise aqueous metal chloride salts.

48. The electrical energy storage system of claim 43, wherein said first optical absorption spectra and said second optical absorption spectra are different.

51. The electrical energy storage system of claim 43, wherein

said first electrolyte is an anolyte comprising an acidic solution comprising

Cr²⁺ and Fe²⁺ in the completely charged state;

Cr³⁺ and Fe²⁺ in the completely discharged state; and

said second electrolyte is a catholyte comprising an acidic solution comprising

Cr³⁺ and Fe³⁺ in the completely charged state; and

Cr³⁺ and Fe²⁺ in the completely discharged state.

53. The electrical energy storage system of claim 43, wherein said spectrophotometer comprises at least one light emitter and at least one light receiver.

55. The electrical energy storage system of claim 53, comprising two light emitters, wherein

one light emitter is for photometry of said first electrolyte;

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one light emitter is for photometry of said second electrolyte.

56. The electrical energy storage system of claim 53, wherein said light emitters emit light as photometric beams with spectral bandwidths less than 50 nm FWHM.

57. The electrical energy storage system of claim 56, further comprising at least one transparent tube, wherein said tube intercepts at least one of said photometric beams.

58. The electrical energy storage system of claim 57, wherein at least one of said electrolytes flows through said transparent tube.

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61. An electrolyte state of charge measuring system comprising:

at least one electrolyte having different optical absorption spectra in reduced and oxidized forms;

a spectrophotometer for measuring the optical absorption spectra of said electrolyte;

a means for correlating the optical absorption spectra of said electrolyte with the state of charge of said electrolyte; and

an output for providing the state of charge to the system.

62. The measuring system of claim 61, wherein said spectrophotometer comprises at least one light emitter and at least one light receiver.

63. The measuring system of claim 62, wherein said light emitters are Light Emitting Diodes (LEDs).

64. The measuring system of claim 62, wherein

said light emitters emit light as photometric beams with narrow, preferably less than 50 nm

FWHM spectral bandwidths;

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said light receivers further comprise at least one filter wherein said filter, filters incoming photometric beams to produce incoming photometric beams with narrow spectral bandwidths.

65. The measuring system of claim 64, further comprising at least one transparent tube, wherein said tube intercepts at least one of said photometric beams.

66. The measuring system of claim 65, wherein at least one electrolyte flows through said transparent tube.

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68. A method for determining the state of charge of an electrolyte, wherein said electrolyte exhibits different optical absorption spectra in oxidized and reduced forms, said method comprising the steps:

a) providing reference optical absorption spectrum of said electrolyte in pure fully oxidized and pure fully reduced forms;

b) providing a test sample of said electrolyte, of which the state of charge is to be determined;

c) measuring the optical absorption spectrum of said test sample of electrolyte;

d) correlating the optical absorption spectrum of said test sample with the optical absorption spectra of said pure oxidized and reduced samples to provide the relative absorptivity of the test sample; and

e) determining the state of charge of the electrolyte from the relative absorptivity of the test sample.

69. The method of claim 68, wherein step a) comprises the steps of

i) providing a pure sample of said electrolyte in fully oxidized form;

ii) measuring the optical absorption spectrum of said pure oxidized electrolyte;

iii) providing a pure sample of said electrolyte in fully reduced form; and

iv) measuring the optical absorption spectrum of said pure reduced electrolyte.

70. The method of claim 68, wherein step e) involves the use of analog circuits, ASICs, mixed signal circuits, algorithms, look up tables or any combination thereof.

71. A method for restoring electrolyte charge balance in a redox system, comprising the steps of:

a) providing a redox system comprising a first electrolyte that exhibits a first optical absorption spectrum and a second electrolyte that exhibits a second optical absorption spectrum;

b) measuring the optical absorption spectra of said electrolytes;

c) determining the state of charge of said electrolytes from the absorption spectra;

d) determining if the state of charge of either said first and/or said second electrolyte falls below predetermined threshold limits; and

e) directing electrolyte flow through a rebalance battery if the state of charge of either said first and/or said second electrolyte falls below said predetermined threshold limits.