An energy storage device comprising at least one negative electrode, wherein each negative electrode is individually selected from (i) an electrode comprising negative battery electrode material; (ii) an electrode comprising capacitor electrode material; (iii) a mixed electrode comprising either—a mixture of battery and capacitor electrode material or—a region of battery electrode material and a region of capacitor electrode material, or—a combination thereof, and wherein the energy storage device either comprises at least one electrode of type (iii), or comprises at least one electrode of each of types (i) and (ii),—at least one positive electrode, wherein the positive electrode comprises positive battery electrode material and a charging ability-increasing additive, such as one or a mixture of: (a) carbon nanomaterial, vapor grown carbon fiber, fullerene, or a mixture thereof, and (b) tin dioxide conductive materials.