The selection and design of catalysts are key factors in determining the performance of lithium-oxygen (Li-O-2) batteries. Among a diverse selection of catalysts, platinum (Pt) is attracting attention as it possesses superior catalytic activity in both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in comparison to other catalysts. Catalytic activity is influenced by various factors related to catalytic active sites, such as the surface area and grain size. Until now, the morphology of Pt catalysts has been limited to spherical shapes; studies on various other morphologies of these catalysts have proven insufficient. In this work, highly monodisperse platinum hole-cylinder nanoparticles (Pt-HCNPs) with a small grain size of 5 nm were fabricated using a top-down method. The Pt-HCNPs were composited with graphene nanoplatelets (GNPs) to achieve a significantly reduced overpotential of 0.41 V and a high energy efficiency of 90%. During discharge, amorphous Li2O2 with a nanoflake morphology that facilitates formation and decomposition was found. This unique Li2O2 formation process is suggested to be a cause of the reduction mechanism that occurs via numerous catalytic active sites provided by the hole-cylinder morphology and small grain size of this catalyst. These findings suggest a strategy for fabricating catalysts for high-performance Li-O-2 batteries through a top-down method known as secondary sputtering lithography.