An object of the invention is to provide an electrode material slurry for preparation of lithium-ion secondary batteries favorable in properties and superior in storage stability and an aqueous binder composition for lithium-ion secondary batteries that can be used for production of lithium-ion secondary batteries superior in discharge rate characteristics and cycle characteristics.Provided is a binder composition for lithium-ion secondary battery electrode, comprising polymer particles containing (a) an ethylenic unsaturated carboxylic ester compound and (b) an ethylenic unsaturated sulfonic acid compound at a (a)/(b) mass ratio of (98 to 91)/(2 to 9) in a total (a) and (b) amount of 70 mass % or more, based on the monomeric raw materials.