A water-based coating formulation for an electrode plate of an electricity storage device, said water-based coating formulation being adapted to form a coating film layer on the electrode plate, comprising: in a water-based medium containing at least water as a polar solvent, as a resin binder, at least one resin having a saponification degree of 40% or higher and selected from the group consisting of unmodified polyvinyl alcohol, modified polyvinyl alcohols, unmodified ethylene-vinyl alcohol copolymer and modified ethylene-vinyl alcohol copolymers, a conductive material, and at least one polybasic acid selected from the group consisting of 1,2,3,4-butanetetracarboxylic acid, pyromellitic acid, citric acid, ethylenediaminetetraacetic acid, 1,2,3-propanetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, trimellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid and 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, or an acid anhydride thereof, wherein as proportions of the components to, the resin binder is from 0.1 to 3 parts by mass and the polybasic acid is from 0.01 to 6 parts by mass, both, per parts by mass of the conductive material, and the coating formulation has a solids content of from 0.02 mass% to 40 mass%; said formulation further comprising at least one additive resin selected from the group consisting of homopolymer of vinylpyrrolidone as a constituent monomer, copolymers of vinylpyrrolidone as an essential constituent monomer, chitosan and chitosan derivatives. in a water-based medium containing at least water as a polar solvent, as a resin binder, at least one resin having a saponification degree of 40% or higher and selected from the group consisting of unmodified polyvinyl alcohol, modified polyvinyl alcohols, unmodified ethylene-vinyl alcohol copolymer and modified ethylene-vinyl alcohol copolymers, a conductive material, and at least one polybasic acid selected from the group consisting of 1,2,3,4-butanetetracarboxylic acid, pyromellitic acid, citric acid, ethylenediaminetetraacetic acid, 1,2,3-propanetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, trimellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid and 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, or an acid anhydride thereof, as a resin binder, at least one resin having a saponification degree of 40% or higher and selected from the group consisting of unmodified polyvinyl alcohol, modified polyvinyl alcohols, unmodified ethylene-vinyl alcohol copolymer and modified ethylene-vinyl alcohol copolymers, a conductive material, and at least one polybasic acid selected from the group consisting of 1,2,3,4-butanetetracarboxylic acid, pyromellitic acid, citric acid, ethylenediaminetetraacetic acid, 1,2,3-propanetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 1,2,4,5-cyclohexanetetracarboxylic acid, trimellitic acid, 1,4,5,8-naphthalenetetracarboxylic acid and 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, or an acid anhydride thereof, wherein as proportions of the components to, the resin binder is from 0.1 to 3 parts by mass and the polybasic acid is from 0.01 to 6 parts by mass, both, per parts by mass of the conductive material, and the coating formulation has a solids content of from 0.02 mass% to 40 mass%; said formulation further comprising at least one additive resin selected from the group consisting of homopolymer of vinylpyrrolidone as a constituent monomer, copolymers of vinylpyrrolidone as an essential constituent monomer, chitosan and chitosan derivatives.