A method of preparing a bimodal positive electrode active material precursor, comprising: inputting a first reaction source material including a first aqueous transition metal solution, an ammonium-cation-containing complex-forming agent, and a basic aqueous solution into a reactor; performing a precipitation reaction at pH 12 or more to induce the nucleation of a first positive electrode active material precursor particle; performing a precipitation reaction at less than pH 12 to induce the growth of the first positive electrode active material precursor particle; inputting a second reaction source material including a second aqueous transition metal solution, an ammonium-cation-containing complex-forming agent, and a basic aqueous solution into the reactor containing the first positive electrode active material precursor particle, wherein the second aqueous transition metal solution has a different metal element composition from that of the first aqueous transition metal solution: performing a precipitation reaction at pH 12 or more to induce the nucleation of a second positive electrode active material precursor particle, performing a precipitation reaction at less than pH 12 to induce the simultaneous growth of the first positive electrode active material precursor particle and the second positive electrode active material precursor particle, thereby preparing a bimodal positive electrode active material precursor including the first positive electrode active material precursor particle and the second positive electrode active material precursor particle, which have different average particle diameters (D 50), wherein at least one of the first aqueous transition metal solution and the second aqueous transition metal solution contains one or more doping elements selected from among Zr, B, W, Mo, Cr, Al, Ti, Mg, Ta, and Nb. inputting a first reaction source material including a first aqueous transition metal solution, an ammonium-cation-containing complex-forming agent, and a basic aqueous solution into a reactor; performing a precipitation reaction at pH 12 or more to induce the nucleation of a first positive electrode active material precursor particle; performing a precipitation reaction at less than pH 12 to induce the growth of the first positive electrode active material precursor particle; inputting a second reaction source material including a second aqueous transition metal solution, an ammonium-cation-containing complex-forming agent, and a basic aqueous solution into the reactor containing the first positive electrode active material precursor particle, wherein the second aqueous transition metal solution has a different metal element composition from that of the first aqueous transition metal solution: performing a precipitation reaction at pH 12 or more to induce the nucleation of a second positive electrode active material precursor particle, performing a precipitation reaction at less than pH 12 to induce the simultaneous growth of the first positive electrode active material precursor particle and the second positive electrode active material precursor particle, thereby preparing a bimodal positive electrode active material precursor including the first positive electrode active material precursor particle and the second positive electrode active material precursor particle, which have different average particle diameters (D 50), wherein at least one of the first aqueous transition metal solution and the second aqueous transition metal solution contains one or more doping elements selected from among Zr, B, W, Mo, Cr, Al, Ti, Mg, Ta, and Nb. performing a precipitation reaction at pH 12 or more to induce the nucleation of a second positive electrode active material precursor particle, performing a precipitation reaction at less than pH 12 to induce the simultaneous growth of the first positive electrode active material precursor particle and the second positive electrode active material precursor particle, thereby preparing a bimodal positive electrode active material precursor including the first positive electrode active material precursor particle and the second positive electrode active material precursor particle, which have different average particle diameters (D 50), wherein at least one of the first aqueous transition metal solution and the second aqueous transition metal solution contains one or more doping elements selected from among Zr, B, W, Mo, Cr, Al, Ti, Mg, Ta, and Nb.