NOVELTY - A paper comprises a silicon-coated web of carbon nanofibers. The carbon nanofibers have a stacked-cup morphology; and have a diameter of less than 100 nm. The porosity of the carbon nanofiber web measured prior to coating with silicon is greater than 50%. The carbon nanofiber web contains a carbonized additive (less than 2 wt.% based on the weight of the web prior to coating with silicon), and metallic nanofibrils.    USE - As an energy storage material, or as an current collector for a battery and an asymmetric electrochemical capacitor (claimed).    ADVANTAGE - The paper has amorphous and/or crystalline silicon content of 10-90 (preferably 15-50) wt.%, and a conductivity of 0.01-100 ohm-1-cm-1; and is 2-20 mils thick. The paper contains silicon coating of 2-200 (preferably 2-50) nm thick; and web having a density of 0.05-0.8 g/cc prior to being coated with silicon. By using a low density nanofiber paper as a substrate, it is possible to create an electrode with a high silicon content, and thus a high energy storage capacity as an anode material in a lithium ion battery, e.g. if a paper consisting of 60 nm diameter nanofibers that individually have a density of 1.6 g/cc is uniformly coated with a 10 nm layer of silicon, the resulting paper would contain Si (49 wt.%) and have a theoretical energy storage capacity as high as 2058 mAh/g due to the silicon content (silicon has a theoretical lithium-ion anode energy storage of -4200 mAh/g). Nanofiber paper substrates have the ability to host a high silicon content in a thin-film form, which promotes cycling stability without a loss of storage capacity, thus provides electrode having good cycling features and high energy storage. The low density nanofiber paper is flexible, e.g. flexibility is useful so that one can coil battery electrodes around small diameter mandrels so that a battery can be manufactured in a jelly roll design. Low density nanofiber paper (prior to coating with silicon) is coiled around a mandrel as thin as 0.25 inches without fracturing.    DESCRIPTION OF DRAWING(S) - The figures show a schematic view of a carbon fiber having a stacked cup structure used in paper, and a scanning electron microscope image of a carbon nanofiber used in paper.