TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The moisture content of the spinel-type lithium manganese transition metal oxide is 0-150 ppm measured at 200-300 degrees C by a Karl Fischer technique. The spinel-type lithium manganese transition metal oxide contains more than 0 wt.% and 0.3 wt.% or less magnesium, 0.4-1.8 wt.%, preferably 0.9-1.8 wt.% aluminum and more than 0 wt.% and 0.3 wt.% less sulfur. The spinel-type lithium manganese transition metal oxide has a complex oxide phase containing nickel, manganese and boron. The amount of magnetically attracted material in the spinel-type lithium manganese transition metal oxide is more than 0 ppb and less than 450 ppb, measured using a 500-cc lidded resin container by adding 500 cc ion-exchange water, one cylindrical-shaped stirring rod-type magnet covered with tetrafluoroethylene to 100 g positive electrode active material (powder), placing on a ball mill rotating stand, rotating, slurrying, taken out magnet, removing excess powder adhered to the magnet by immersing in ion-exchange water with the ultrasonic washing machine, taken out magnet, dissolving a magnetically attracted material in aqua regia, heating at 80 degrees C for 30 minutes in aqua regia, analyzing amount of zinc, iron and chromium in the aqua regia in which the magnetically attracted material is dissolved by inductively-coupled-plasma-atomic-emission-spectrometry apparatus, and calculating obtained total amount of per positive electrode active material weight as the amount of magnetically attracted material. The magnet has a magnetic force of 100-150 mT when magnetic force is measured using TM-601-type tesla meter. The spinel-type lithium manganese transition metal oxide comprises composition of formula: Li1+xM2-xO4 (I), or Li(LiaMn2-a-b-cM1bM2c)O4-( delta ) (II).M=transition metal chosen from Mn, Al and Mg;x=0.01-0.09, preferably 0.01-0.08;M1=metallic element chosen form Ni, Co and Fe;M2=metallic element chosen form Mg, Ti, Al, Ba, Cr and Nb;a=0.00-1;b=0.3-0.7;andc,( delta )=0 or more.