NOVELTY - Electrochemical cell (I), comprises a housing having disposed in it, an electrolyte, and a multi-layer article at least partially immersed in the electrolyte, where the article comprises a first metallic current collector, first electrode material in electrically conductive contact with the collector, second electrode material in ionically conductive contact with the first electrode material, porous separator (1) disposed between and contacting the first- and second-electrode material, and a second metallic current collector in electrically conductive contact with second electrode material.    USE - (I) is useful in consumer electronics, power tools, and hybrid electric vehicles. The multi-layer article is useful in batteries and capacitors, preferably electronic double layer capacitors.    ADVANTAGE - The article has a polyimide nanoweb separator, which exhibits high strength and toughness, low solvent absorption, and high strength retention after solvent exposure compared to the conventional polyimide nanoweb separators. The polyimide nanoweb separator: exhibits good electrochemical stability and performance; and exhibits electrolyte uptake below 20 wt% after 1300 hours of exposure. The nanoweb separator provides lithium ion batteries with superior durability in regard to both thermal stress and mechanical shock compared to conventional batteries. (I) has charge/discharge/recharge hysteresis, first cycle irreversible capacity loss, and thermal stability.    DETAILED DESCRIPTION - Electrochemical cell (I), comprises a housing having disposed in it, an electrolyte, and a multi-layer article at least partially immersed in the electrolyte, where the multi-layer article comprises a first metallic current collector, first electrode material in electrically conductive contact with the first metallic current collector, second electrode material in ionically conductive contact with the first electrode material, porous separator (1) disposed between and contacting the first electrode material and the second electrode material, and a second metallic current collector in electrically conductive contact with the second electrode material, where the porous separator comprises a nanoweb that comprises many nanofibers, where the nanofibers essentially comprise a fully aromatic polyimide.    DESCRIPTION OF DRAWING(S) - The figure is a schematic depiction of the multi-layer article.    Porous nanoweb separator (1)    Negative electrode (2)    Positive electrode (3)    Copper foil (4a)    Aluminum foil (4b)