Energy storage device including a redox-enhanced electrolyte
An electrical double layer capacitor (EDLC) energy storage device is provided that includes at least two electrodes and a redox-enhanced electrolyte including two redox couples such that there is a different one of the redox couples for each of the electrodes. When charged, the charge is stored in Faradaic reactions with the at least two redox couples in the electrolyte and in a double-layer capacitance of a porous carbon material that comprises at least one of the electrodes, and a self-discharge of the energy storage device is mitigated by at least one of electrostatic attraction, adsorption, physisorption, and chemisorption of a redox couple onto the porous carbon material.
1. An energy storage device, comprising:
an electrical double layer capacitor (EDLC) including at least two electrodes separated by a redox-enhanced electrolyte having an integral active component for storing a charge;
wherein the redox-enhanced electrolyte includes at least two redox couples, such that there is a different one of the redox couples for each of the electrodes;
wherein, when charged, the charge is stored in Faradaic reactions with the at least two redox couples in the electrolyte and in a double-layer capacitance of a porous carbon material that comprises at least one of the electrodes; and
wherein a self-discharge of the energy storage device is mitigated by at least one of electrostatic attraction, adsorption, physisorption, and chemisorption of a redox couple onto the porous carbon material.
2. The energy storage device of claim 1 , wherein the at least two redox couples are mixed into the electrolyte and the EDLC does not include an ion-selective separator.
3. The energy storage device of claim 1 , wherein the at least two redox couples do not comprise a metal.
4. The energy storage device of claim 1 , wherein at least one redox couple comprises a viologen.
5. The energy storage device of claim 1 , wherein at least one redox couple comprises Bromine.
6. The energy storage device of claim 1 , wherein the electrolyte is an aqueous, organic or ionic liquid.
7. The energy storage device of claim 1 , wherein a PH of the redox-enhanced electrolyte, concentrations and ratios of the at least two redox couples, and/or a porosity of the porous carbon material, are adjusted to control an internal self-discharge of the electrical double layer capacitor.
8. The energy storage device of claim 1 , wherein each of the at least two redox couples operates at a different potential.
9. The energy storage device of claim 1 , wherein the redox couples comprise any couple with a standard reduction potential within an operating voltage window of the electrical double layer capacitor.
10. A method for fabricating an energy storage device, comprising:
fabricating an electrical double layer capacitor (EDLC) including at least two electrodes separated by a redox-enhanced electrolyte that comprises an integral active component for charge storage,
wherein:
at least one electrode comprises is fabricated from porous conductive carbon material;
the redox-enhanced electrolyte is fabricated to include at least two redox couples, such that there is a different one of the redox couples for each of the electrodes;
charge is stored in Faradaic reactions with the at least two redox couples in the electrolyte; and
the redox couples comprise compounds having properties selected to inhibit internal self-discharge within the electrical double layer capacitor.
11. The method of claim 10 , further comprising adjusting a PH of the redox-enhanced electrolyte, concentrations and ratios of the at least two redox couples, and/or a porosity of the porous carbon material, to control an internal self-discharge of the electrical double layer capacitor.
12. The method of claim 10 , wherein the redox couples comprise compounds selected for their ability to mitigate self discharge of the device via electrostatic attraction adsorption, physisorption and/or chemisorption onto the porous conductive carbon material.
13. The method of claim 10 , wherein:
(a) the device does not comprise an ion-selective separator;
(b) the at least two redox couples do not comprise a metal;
(c) at least one redox couple comprises a viologen; and/or
(d) the electrolyte is an aqueous liquid.
14. The method of claim 10 , wherein the device delivers an energy density of at least at least 10 Wh kg-1 based on the mass of electrodes and electrolyte.
15. The method of claim 10 , wherein the device exhibits a self-discharge rate of less than 50 percent after three hours at open circuit.
16. A method of inhibiting internal self-discharge of an energy storage device, wherein the device comprises:
at least two electrodes, wherein at least one electrode comprises a porous carbon material; and
an aqueous redox-enhanced electrolyte comprising a first redox active compound and a second redox active compound, wherein the electrolyte functions as an active component for charge storage, the method comprising:
allowing the first redox active compound and/or the second redox active compound to adsorb to the porous carbon material via electrostatic attraction adsorption, physisorption and/or chemisorption, thereby mitigating self-discharge of the device so that internal self-discharge of the energy storage device in inhibited.
17. The method of claim 16 , wherein the device is an electrical double layer capacitor.
18. The method of claim 16 , wherein the device does not include an ion-selective separator.
19. The method of claim 16 , wherein a first redox active couple and a second redox active compound do not include a metal other than potassium.
20. The method of claim 16 , wherein at least one redox active compound includes a viologen.