A relatively thin planar anode for use in a wet electrolytic capacitor is provided. Through a combination of specific materials and processing techniques, the present inventors have surprisingly discovered that the resulting anode may possess a high volumetric efficiency, yet still be able to operate at a high voltage and capacitance, resulting in a capacitor with a high energy density. The anode is a pressed pellet formed from an electrically conductive powder that contains a plurality of particles (including agglomerates thereof) having a flake-like morphology. The present inventors have discovered that such a morphology can optimize packing density, which reduces the thickness of the anode and improves volumetric efficiency. Such particles can provide a short transmission line between the outer surface and interior of the anode and a highly continuous and dense wire-to-anode connection with high conductivity. The particles may also increase the breakdown voltage and help lower ESR.