Stable bromine charge storage in porous carbon electrodes using tetraalkylammonium bromides for reversible solid complexation
Electrolytes for use in electric double-layer capacitors (EDLCs; often referred as supercapacitors or ultracapacitors) are disclosed. In one example, the electrolyte comprises viologen in both the anolyte and the catholyte (with bromide). In another example, the electrolyte comprises viologen (in the anolyte) and tetraalkylammonium with bromide (in the catholyte), wherein the tetraalkylammonium is used to achieve solid complexation of bromine in the activated carbon of the cathode. In a third example, a zinc bromine/tetraalkylammonium supercapacitor/battery hybrid is disclosed. Also disclosed is a corrosion resistant bipolar pouch cell that can be used with the electrolyte embodiments described herein.
1. An energy storage device, comprising:
an electrical double layer capacitor (EDLC) including:
one or more cells, each cell including:
a pouch having a first wall and a second wall, the first wall and the second wall each comprising a current collector including a carbon-polymer composite; a plastic spacer, a first electrode, a second electrode , an electrolyte, and a separator inside the pouch; and
a seal between the first wall and the second wall so that the plastic spacer, the first electrode, the second electrode, the electrolyte, and the separator are sealed inside the pouch; and wherein:
the first electrode and the second electrode are in contact with the electrolyte,
the electrolyte includes a first redox couple comprising bromine or a bromine moiety and a second redox couple comprising a viologen;
during charging, the electrolyte evolves into a catholyte including the first redox couple and an anolyte including the second redox couple; and
when charged, the charge is stored in Faradaic reactions with the first redox couple and the second redox couple in the electrolyte and in a double-layer capacitance of athc porous carbon material that comprises at least one of the first electrodecicctrodcs or the second electrode.
2. The device of claim 1 , wherein the viologen has the structure:
and
R is an alkyl.
3. The device of claim 2 , wherein the viologen comprises at least one compound selected from ethyl viologen, butyl viologen, and pentyl viologen.
4. The device of claim 1 , wherein the catholyte further comprises a viologen.
5. The device of claim 1 , wherein the electrolyte further comprises a complexing agent comprising a viologen that forms a complex with the bromine moiety in the catholyte.
6. The device of claim 5 , wherein the viologen is at least one compound selected from hexyl viologen and pentyl viologen.
7. The device of claim 5 , wherein the viologen forming a complex with the bromine moiety has the structure:
and
R is an alkyl having at least 4 carbons.
8. The device of claim 1 , wherein the seal is a heat seal and the carbon-polymer composite is a thermoplastic.
9. The device of claim 8 , wherein the separator and the plastic spacer are made from one component with a microporous polymer separator that has porosity collapse in the region of the heat-seal.
10. The device of claim 1 , wherein the first and second walls are flexible and each have a thickness of 100 micrometers or less.
11. The device of claim 1 , further comprising a compartment housing the first electrode, the second electrode, the separator, and the electrolyte permeating the electrodes and separator, wherein the compartment is bound above and below by the walls and on the edges by the inside of the plastic spacer.
12. The device of claim 1 , comprising a plurality of the cells stacked on top of one another in a series configuration, wherein the positive current collector of one cell and the negative current collector of the adjacent cell are replaced by a single bipolar current collector made of the carbon-polymer composite.
13. The device of claim 1 , wherein the first redox couple further comprises a complexing agent comprising a tetraalkylammonium that forms a complex with the bromine or the bromine moiety in the catholyte.
14. The device of claim 13 , wherein the tetraalkylammonium is tetrabutylammonium bromide.
15. The device of claim 14 , wherein:
the tetrabutylammonium bromide combines with the bromine moiety to form a [TBA + ·Bra 3 − ] solid complex retained in the pores of the porous carbon material of the electrode comprising a cathode.
16. The device of claim 1 , wherein the electrolyte further comprises a complexing agent comprising a viologen that forms a complex with the bromine or the bromine moiety in the catholyte.
17. An energy storage device, comprising:
one or more cells, each cell including:
a pouch having a first wall and a second wall, the first wall and the second wall each comprising a current collector including a carbon-polymer composite; a plastic spacer, a first electrode, a second electrode , an electrolyte, and a separator inside the pouch; and
a seal between the first wall and the second wall so that the plastic spacer, the first electrode, the second electrode, the electrolyte, and the separator are sealed inside the pouch; and wherein:
the electrolyte includes zinc halide,
the electrodes comprise a cathode and an anode, the cathode comprising carbon, tetraalkylammonium complexing agent is pre-soaked on the carbon in the cathode, and
during charging, the zinc from the zinc halide plates onto the anode and the halogen in the halide oxidizes so as to form a solid complex with the tetraalkylammonium on the cathode.
18. The energy storage device of claim 17 , wherein the carbon in the cathode is soaked with the tetraalkylammonium complexing agent and the tetraalkylammonium complexing agent is tetrabutylammonium bromide or cetyltrimethylammonium bromide.
19. The energy storage device of claim 17 , wherein the electrolyte does not include a viologen.