A polyimide binder for energy storage device, which is obtained by subjecting an aqueous solution of a polyamic acid comprising a repeating unit represented by the following general formula (I) to an imidization reaction, the polyimide having a tensile elastic modulus of 1.5 GPa or more and 2.3 GPa or less: wherein A is one or more selected from a tetravalent group resulting from eliminating a carboxyl group from an aromatic tetracarboxylic acid not containing a fluorine group, a tetravalent group resulting from eliminating a carboxyl group from an aliphatic tetracarboxylic acid, and a tetravalent group resulting from eliminating a carboxyl group from an aromatic tetracarboxylic acid containing a fluorine group; and B is one or more selected from a divalent group resulting from eliminating an amino group from an aromatic diamine not containing a fluorine group, whose solubility in water of 25°C is 0.1 g/L or more, a divalent group resulting from eliminating an amino group from an aliphatic diamine having a molecular weight of 500 or less, and a divalent group resulting from eliminating an amino group from an aromatic diamine containing a fluorine group, provided that 55 mol% or more of B in a total amount of the repeating unit is the divalent group resulting from eliminating an amino group from an aliphatic diamine having a molecular weight of 500 or less; wherein the aqueous solution of the polyamic acid is one obtained by allowing a tetracarboxylic acid component and a diamine component to react with each other by using water as a reaction solvent in the presence of an imidazole; wherein the tetracarboxylic acid component of the polyamic acid is one or more selected from 4,4'-oxydiphthalic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 1,2,4,5-cyclohexane tetracarboxylic acid-1,2:4,5-dianhydride, and dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride; wherein the diamine component of the polyamic acid is one or more selected from p-phenylenediamine, 4,4'-diaminodiphenyl ether, trans-1,4-diaminocyclohexane, cis-1,4-diaminocyclohexane, 1,6-hexamethylenediamine, and 1,4-bis(aminomethyl)cyclohexane. A is one or more selected from a tetravalent group resulting from eliminating a carboxyl group from an aromatic tetracarboxylic acid not containing a fluorine group, a tetravalent group resulting from eliminating a carboxyl group from an aliphatic tetracarboxylic acid, and a tetravalent group resulting from eliminating a carboxyl group from an aromatic tetracarboxylic acid containing a fluorine group; and B is one or more selected from a divalent group resulting from eliminating an amino group from an aromatic diamine not containing a fluorine group, whose solubility in water of 25°C is 0.1 g/L or more, a divalent group resulting from eliminating an amino group from an aliphatic diamine having a molecular weight of 500 or less, and a divalent group resulting from eliminating an amino group from an aromatic diamine containing a fluorine group, provided that 55 mol% or more of B in a total amount of the repeating unit is the divalent group resulting from eliminating an amino group from an aliphatic diamine having a molecular weight of 500 or less; wherein the aqueous solution of the polyamic acid is one obtained by allowing a tetracarboxylic acid component and a diamine component to react with each other by using water as a reaction solvent in the presence of an imidazole; wherein the tetracarboxylic acid component of the polyamic acid is one or more selected from 4,4'-oxydiphthalic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 1,2,4,5-cyclohexane tetracarboxylic acid-1,2:4,5-dianhydride, and dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride; wherein the diamine component of the polyamic acid is one or more selected from p-phenylenediamine, 4,4'-diaminodiphenyl ether, trans-1,4-diaminocyclohexane, cis-1,4-diaminocyclohexane, 1,6-hexamethylenediamine, and 1,4-bis(aminomethyl)cyclohexane. <EOS>