In order to enhance the utilization of active cathode material in lithium rechargeable batteries, physical mixtures of mu m-sized LiCoO2 (LCO) and nm-sized Li[Co0.1Ni0.15Li0.2Mn0.55]O-2 (LCMNO) were prepared by varying the LCO content, and the physical and electrochemical properties of lithium half-cells utilizing the mixed cathodes were characterized. Our main concern is the packing state between the microparticles and nanoparticles within the electrode, which influences the determination of the electrode density. We found that the electrode composed of 80 wt.% LCO and 20 wt.% LCMNO shows the best performance in capacity retention ratio and high-rate capability, which are comparable to those of LCMNO, due to the superior density in the electrode's packing state over other samples.