Conductive coating for use in electrolytic capacitors
A dispersion that contains an intrinsically conductive polythiophene formed via poly(ionic liquid)-mediated polymerization is provided. Without intending to be limited by theory, it is believed that a thiophene monomer can polymerize along the chains of a poly(ionic liquid). In this manner, the poly(ionic liquid) may act as a template for polymerization to provide a particle dispersion that is substantially homogeneous and stable. Such dispersions may be employed in an electrolytic capacitor as a solid electrolyte and/or as a conductive coating that is electrical communication with the electrolyte. Regardless, the dispersion may be more easily and cost effectively formed and incorporated into the structure of the capacitor. Moreover, due to the presence of the ionic liquid, the dispersion is conductive and does not require the addition of conventional dopants, such as polystyrene sulfonic acid. For example, the dispersion may have a specific conductivity, in the dry state, of about 1 Siemen per centimeter (“S/cm”) or more, in some embodiments about 10 S/cm or more, in some embodiments about 20 S/cm or more, and in some embodiments, from about 50 to about 500 S/cm.
1. An electrolytic capacitor comprising:
an anode body;
a dielectric overlying the anode body; and
a conductive coating that overlies the dielectric, wherein the conductive coating contains particles formed from a poly(ionic liquid) and an intrinsically conductive polythiophene.
2. The electrolytic capacitor of claim 1 , wherein the poly(ionic liquid) contains repeating units of a monomer that includes at least one heteroatom as a cationic center and a counterion.
3. The electrolytic capacitor of claim 2 , wherein the monomer has one of the following structures:
wherein, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 are independently selected from the group consisting of hydrogen; substituted or unsubstituted C 1 -C 10 alkyl groups; substituted or unsubstituted C 3 -C 14 cycloalkyl groups; substituted or unsubstituted C 1 -C 10 alkenyl groups; substituted or unsubstituted C 2 -C 10 alkynyl groups; substituted or unsubstituted C 1 -C 10 alkoxy groups; substituted or unsubstituted acyloxy groups; substituted or unsubstituted aryl groups; substituted or unsubstituted heteroaryl groups; and combinations thereof.
4. The electrolytic capacitor of claim 2 , wherein the monomer includes a heteroaryl group, heterocyclic group, or a combination thereof.
5. The electrolytic capacitor of claim 2 , wherein the monomer has the structure (I):
wherein,
R 1 , R 2 , R 4 , and R 5 are independently a C 1 -C 6 alkyl; and
R 3 and R 6 are each hydrogen.
6. The electrolytic capacitor of claim 2 , wherein the monomer has the structure (II):
wherein,
R 1 and R 4 are independently a C 1 -C 6 alkyl; and
R 2 , R 3 , R 5 , and R 6 are each hydrogen.
7. The electrolytic capacitor of claim 2 , wherein the monomer has the structure (III):
wherein,
R 1 and R 5 are independently a C 1 -C 6 alkyl;
R 2 , R 3 , and R 4 are each hydrogen.
8. The electrolytic capacitor of claim 2 , wherein the monomer is diallyldimethylammonium, 1-methyl-4-vinylpyridinium, 1-vinyl-3-ethylimidazolium, or a combination thereof.
9. The electrolytic capacitor of claim 2 , wherein the counterion includes a halogen, sulfate, sulfonate, sulfosuccinate, amide, imide, borate, phosphate, phosphinate, antimonite, aluminate, fatty acid carboxylate, cyanate, acetate, or a combination thereof.
10. The electrolytic capacitor of claim 9 , wherein the counterion includes chloride, bromide, hexafluorophosphate, bis(pentafluoroethylsulfonyl)imide, oleate, or a combination thereof.
11. The electrolytic capacitor of claim 1 , wherein the polythiophene has the following structure:
wherein,
T is O or S;
D is an optionally substituted C 1 to C 5 alkylene radical;
R 7 is a linear or branched, optionally substituted C 1 to C 18 alkyl radical; optionally substituted C 5 to C 12 cycloalkyl radical; optionally substituted C 6 to C 14 aryl radical; optionally substituted C 7 to C 18 aralkyl radical; optionally substituted C 1 to C 4 hydroxyalkyl radical, or hydroxyl radical; and
q is an integer from 0 to 8.
12. The electrolytic capacitor of claim 11 , wherein the polythiophene has the following structure:
13. The electrolytic capacitor of claim 1 , wherein the polythiophene is poly(3,4-ethylenedioxythiophene).
14. The electrolytic capacitor of claim 1 , wherein the poly(ionic) liquid includes poly(diallyldimethylammonium chloride); poly(1-methyl-4-vinyl pyridinium bromide); poly(1-vinyl-3-ethylimidazolium bromide); poly(diallyldimethylammonium)-bis(pentafluoroethylsulfonyl)imide; poly(1-methyl-4-vinylpyridinium)oleate; poly(1-vinyl-3-ethylimidazolium)hexafluorophosphate; or a combination thereof.
15. The electrolytic capacitor of claim 1 , wherein the particles have an average size of from about 1 to about 200 nanometers.
16. The electrolytic capacitor of claim 1 , wherein the conductive coating is positioned adjacent to the dielectric of the capacitor.
17. The electrolytic capacitor of claim 1 , further comprising a solid electrolyte that overlies the dielectric, wherein the conductive coating overlies both the dielectric and the solid electrolyte.
18. The electrolytic capacitor of claim 17 , wherein the solid electrolyte contains a conductive polymer.
19. The electrolytic capacitor of claim 1 , wherein the conductive coating is generally free of poly(styrene sulfonic acid).
20. The electrolytic capacitor of claim 1 , wherein the anode body includes tantalum, niobium, or an electrically conductive oxide thereof.
21. A method of forming a solid electrolytic capacitor, the method comprising applying a dispersion to a capacitor element that comprises an anode body and a dielectric, wherein the dispersion includes a solvent and particles formed from a poly(ionic liquid) and an intrinsically conductive polythiophene.
22. The method of claim 21 , wherein the particles constitute from about 0.1 wt. % to about 10 wt. % of the dispersion.
23. The method of claim 21 , wherein the solvent includes water.
24. The method of claim 23 , wherein water constitutes at least about 50 wt. % of solvents present in the dispersion.
25. The method of claim 21 , wherein organic solvents constitute at least about 50 wt. % of solvents present in the dispersion.
26. The method of claim 21 , wherein the capacitor element further comprises a solid electrolyte that overlies the dielectric, and wherein the dispersion is applied over the solid electrolyte.