NOVELTY - The stirrer comprises a pre-mixer that mixes ferric solution and lithium solution. A supercritical water tube provides supercritical water to a main mixer for agitating the ferric solution and the lithium solution. A static mixer is installed at supercritical flow of the supercritical water tube. A cooling apparatus is installed in the supercritical water tube for reducing the heat generated in the main mixer and the pre-mixer. A central tube uniformly mixes the ferric solution and the lithium solution through the center of the main mixer.    USE - The stirrer is useful for producing cathode active material (claimed) that is useful in a lithium-ion secondary battery used in a mobile apparatus and hybrid or electric vehicles.    ADVANTAGE - The stirrer minimizes stirring ratio so that the concentration of the mixture and the supercritical water can be regularly maintained in the mixing process. The pre-mixer can segregate the ferric salt in the ferric solution and lithium solution in the introduction line due to the application of the supercritical water so that the cathode active material is smoothly produced with high quality.    DETAILED DESCRIPTION - The stirrer comprises a pre-mixer that mixes ferric solution and lithium solution. A supercritical water tube provides supercritical water to a main mixer for agitating the ferric solution and the lithium solution. A static mixer is installed at supercritical flow of the supercritical water tube. A cooling apparatus is installed in the supercritical water tube for reducing the heat generated in the main mixer and the pre-mixer. A central tube uniformly mixes the ferric solution and the lithium solution through the center of the main mixer. The central tube is symmetrically connected to both sides of the supercritical water tube. The supercritical water tube is inclinedly connected to an extension direction of the central tube and to form an acute angle. The static mixer is installed in the main mixer from the central tube and a spot in which the supercritical water tube is united according to the flow direction of the supercritical water. The pre-mixer is passed through the center of the central tube. A lithium solution tube is inclinedly connected in both sides of the premixer. The number of active elements in the static mixer is 2-12.