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Abstract

A dendritic sponge which is directionally-grown on a substrate material has a high surface to volume ratio and is suitable for forming anodes for highly efficient capacitors. A dielectric film is formed on the sponge surface by oxidizing the surface. In a preferred embodiment, the dielectric is grown on titanium sponge and is doped with oxides of Ca, Mg, Sr, Be, or Ba to improve the film's dielectric constant or with higher valent cations, such as Cr.sup.6+, V.sup.5+, Ta.sup.5+, Mo.sup.6+, Nb.sup.5+, W.sup.6+, and P.sup.5+, to reduce the oxygen vacancy concentration and leakage current of the dielectric film. A capacitor formed from the sponge includes a cathode electrolyte which serves as an electrical conductor and to repair the dielectric film by re-oxidizing the anode surface at areas of local breakdown. Sponges of titanium, tantalum, and aluminum form efficient dielectric films. In another embodiment, sponges of elements which do not form efficient dielectric films are coated with a dielectric material. Capacitors formed with titanium sponges have energy densities of 10.sup.-2 to 50 Watt hours and power densities of 100,000 to 10,000,000 Watts per kilogram of titanium.

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First Claim