Lithium ion battery and cathode active material therefor

A method for producing manganese-based olivine structural small particles contained in a bimodal-type cathode active material for a lithium ion battery, the cathode active material comprising a mixture of layered LiCoO2 large particles having an average particle diameter of 16 to 25 μm and the manganese-based olivine structural small particles having an average particle diameter of 1 to 3 μm, the manganese-based olivine structural small particles are represented by chemical formula LiCoxMnyFezPO4 (0≤x≤1, 0<y≤1, 0≤z≤1, x+y+z=1), the method comprising:

• a) preparing a precursor aqueous solution by mixing Co(CH3COO)2.4H2O, Mn(CH3COO)2.4H2O, and Fe(NO3)3.9H2O in accordance with a molar ratio;
• b) forming a solid solution of Co, Mn, and Fe by mixing and stirring the precursor aqueous solution with N,N-dimethylformamide (DMF);
• c) forming LiCoxMnyFezPO4 primary particles by introducing H3PO4, lithium hydroxide monohydrate (LiOH.H2O), and ascorbic acid (C6H8O6) into the solid solution;
• and
• d) forming LiCoxMnyFezPO4 secondary particle aggregation by injecting nitric acid (HNO3) into the LiCoxMnyFezPO4 primary particles, adjusting pH, and using a solvothermal synthesis technique.