The present invention provides a composition for electricity storage devices, which is excellent in terms of flexibility, rubbing resistance and particle fall-off, and which is capable of producing an electricity storage device electrode that exhibits good charge and discharge durability characteristics. A composition for electricity storage devices according to the present invention contains a polymer (A) and a liquid medium (B); and the polymer (A) contains 20-70 parts by mass of a repeating unit (a1) that is derived from a conjugated diene compound and 10-50 parts by mass of a repeating unit (a2) that is derived from an unsaturated carboxylic acid if the total of repeating units contained in the polymer (A) is taken as 100 parts by mass. With respect to the integral molecular weight distribution curve of the polymer (A) as determined by size exclusion chromatography (SEC) in accordance with JIS K7252, a copolymer fraction having a molecular weight of 1,000,000 or less is contained in an amount of 30% by mass or more relative to all copolymers.