NOVELTY - A battery electrode (1) comprises an active material layer (3) formed on a surface (2A) of a collector (2), and including an active material, and a conductive additive having a bulk density, which is gradually decreased in a direction from a collector side (3B) of the active material layer to a surface side (3A) of the active material layer. The active material layer includes a first active material sublayer, and a second active material sublayer between the collector and the first active material sublayer.    USE - The battery electrode (i.e. positive and/or negative electrodes) is used for lithium ion secondary battery useful for a battery module for use in a vehicle (claimed). The lithium ion secondary battery (e.g. flat stack bipolar/non-bipolar lithium ion secondary battery) is used for pack batteries useful for battery module. It is used for vehicle driving power source or auxiliary power source. Uses include but are not limited to electric car, hybrid electric car, fuel cell car, hybrid fuel cell car, commercial vehicle (e.g. bus), truck, motor bike, three wheelers, power sources of mobile bodies such as electric trains, and installed power sources such as non-outage power source.    ADVANTAGE - The battery electrode is capable of improving output density of lithium ion secondary battery. It uses a polymer electrolyte for an electrolyte layer, where the battery electrode can bring about high output while keeping an energy density. Voidage in the active material layer is increased in the direction from the collector side of the active material layer to the surface side of the active material layer, so that even a high-viscosity polymer electrolyte can effectively permeate in the active material layer, thus preparing a high-capacity battery. In the case of adjusting the voidage, binder content does not need to increase, thus contributing to increasing capacity of the battery. The active material layer can follow volume expansion which may be caused when contacting the electrolyte, thus preventing exfoliation of the active material layer. Even when a gel electrolyte, which is relatively high in viscosity, is used for an electrolyte layer, a good electrode reaction can be accomplished. Even when a polymer electrolyte, which is relatively low in ion conductivity, is used for the electrolyte layer, an ion conduction path can be smoothened, thus improving output. Using one type of conductive additive can form the active material layer having a stack of sublayers having different voidages, lowering material cost.    DETAILED DESCRIPTION - The bulk density of the conductive additive of the first active material sublayer is smaller than the bulk density of the conductive additive of the second active material sublayer. The bulk density of the conductive additive of the first active material sublayer is 0.01-0.05 g/ml. The active material layer (3) has a thickness of 20-500 mu m. Each of the active material sublayers has a thickness of 10-100 mu m. INDEPENDENT CLAIMS are included for:    (1) a method of producing a battery electrode (1) comprising preparing n types of slurries, each including an active material, a conductive additive, and a solvent, where slurry preparation step is implemented by using n types of the conductive additives having different bulk densities, where n is greater than or equal to 2; applying the slurries in an order of the bulk densities of the included conductive additives to a surface (2A) of a collector (2), where the order is from larger to smaller; forming a coated film including n sublayers, where n is greater than or equal to 2; and pressing the coated film in a stack direction; and    (2) a lithium ion secondary battery comprising a unit cell layer(s) including a positive electrode, an electrolyte layer, and a negative electrode, which are stacked, where the positive and/or negative electrodes are the battery electrode.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic cross-sectional view of a battery electrode.    Battery electrode (1)    Collector (2)    Collector surface (2A)    Active material layer (3)    Surface side (3A)    Collector side (3B)