TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The mixing weight ratio of fine particles (A,B) is 20:1-1:20. Preferred Conditions: The lithium compound, transition-metal compound, and additive are mixed in a liquid medium such that the refractive index is 1.24 as measured using laser diffraction/scattering type particle size distribution measuring device. The mixture is pulverized to a median diameter of 0.4 mu m or less after ultrasonic dispersion (output 30 W, frequency 22.5 kHz) for 5 minutes, by making the particle-diameter reference as volume reference. Spray-drying is carried out at a slurry viscosity of 50-4000 cp. The ratio of gas feed rate (L/minute) and slurry feed rate (L/minute) during spray-drying is set to 1500-5000. The spray-dried fine particles are baked at 950 degrees C or more in an oxygen-containing gas atmosphere. Preferred Additive: The additive is an oxide containing molybdenum, tungsten, niobium, tantalum and/or rhenium. Preferred Particles: Fine particles (A) contain lithium-nickel-manganese-cobalt group complex oxide having crystal structure belonging to layer structure. Fine particles (A) have a composition of formula: LiMO2. The molar ratio of manganese and nickel is 0.8-5, the molar ratio of cobalt with respect to total content of manganese, nickel and cobalt is 0-0.35, and the molar ratio of lithium in element (M) is 0.001-0.02. Fine particles (B) have a composition of formula: Li(Mn2-x'-y'Lix'M'y')O4.M=lithium, nickel and/or manganese, or lithium, nickel, manganese and/or cobalt, preferably Liz/(2+z)((Ni(1+y)/2Mn(1-y)/2)1-xCox)2/(2+z);x=0-0.1;y=-0.1 to 0.1;z=((1-x)(0.05-0.98y)-(1-x)(0.2-0.88y));M'=metallic element(s) which can be substituted by Mn (16d) sites other than Mn and Li;x'=0.01-0.1;andy'=0.01-0.5.Preferred Properties: The positive electrode active material has a refractive index of 1.24, a median diameter of 0.5-10 mu m, a BET specific surface area of 0.5-5 m2/g, a volume density of 0.5-2.5 g/cm3, a volume resistivity of 50-1x 106 Omega .cm when compacted by applying a pressure of 40 MPa, and a carbon concentration of 0.005-0.1 wt.%.