Electrolytic capacitor and large surface area electrode element therefor

DETAILED DESCRIPTION The present invention contemplates a new capacitor electrode element for improving the capacitance per unit volume or weight of an electrolytic capacitor.
The capacitor electrode element in accordance with the invention comprises an electrode body having a plurality of elongated, preferably ribbon-shaped filaments of Al and X, where X is selected from the group consisting of Nb and Ta, interspersed and aligned along an axis of the body.
The electrode body includes an electrode surface comprising exposed surfaces (e.
g.
, exposed ends) of the Al filaments and exposed lengths of the X filaments protruding beyond the exposed surfaces of the Al filaments.
The exposed surfaces of the Al filaments and the exposed lengths of the X filaments number in the millions on the electrode surface to provide an extremely large electrode surface area.
Ribbon-shaped filaments of Al and X preferably exhibiting a thickness of about 0.
01 micron to about 0.
50 micron are preferred to this end.
The exposed surfaces of the Al filaments and the exposed lengths of the X filaments have thin dielectric oxides of Al and X, respectively, formed thereon so as to constitute the dielectric layer of the electrolytic capacitor.
Interfilament interstices disposed between the exposed lengths of the X filaments receive a solid electrolyte (e.
g.
, manganese dioxide) or a liquid electrolyte (e.
g.
, an appropriate ionic salt dissolved in a non-aqueous solvent such as dimethyl formamide) in contact with the dielectric oxides of Al and X.
A cathode electrode is placed in electrically conductive relation to the dielectric oxides of Al and X via the electrolyte.
Electrolytic capacitors in accordance with the invention exhibit highly useful capacitance values (CV/g where C is capacitance in micro-farads, V is the formation voltage of the dielectric oxide films on the electrode surface and g is the mass in grams of the capacitor) at least equivalent to those obtainable from sintered, powder metal electrolytic capacitors heretofore used