NOVELTY - The power storage device has a negative electrode (206b) including a layer of active material (202). The active material layer has a common portion (202a), protrusions (202b) protruding from the common portion, a first insulating layer over the first protrusion, and a second insulating layer over the second protrusion. A positive electrode is in contact with the first insulating layer and the second insulating layer. The insulating layers include a material which has an insulating property and does not react with the electrolyte. The active material is silicon.    USE - Power storage device e.g. lithium-ion secondary battery, lithium-ion capacitor, air cell used for e.g. electronic device. Can also be used in used in vehicle, display device, lighting device. Uses include but are not limited to personal computer, image reproduction device, mobile phone, portable game machine, portable information terminals, electronic-book reader, video camera, digital still camera, high-frequency heating apparatus such as microwave, electric rice cooker, electric washing machine, air-conditioning system such as air conditioner, electric refrigerator, electric freezer, electric refrigerator-freezer, freezer for preserving DNA, dialysis device, electric vehicle, hybrid vehicle, motorized bicycle.    ADVANTAGE - Enhances reliability of battery characteristics since local reaction in the positive electrode and the negative electrode is reduced, reaction between carrier ions and the active material occurs uniformly, and diffusion overvoltage is prevented by providing the insulation layers. Prevents reduction in charge/discharge capacity of the power storage device since protrusions are not in contact with each other and are prevented from being broken.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the negative electrode.    Active material (202)    Common portion (202a)    Protrusions (202b)    Graphene (204)    Negative electrode (206b)    Protective layer (207)