To improve the electrochemical properties of LiNi1/3Co1/3Mn1/3O2 (NCM) under the high-voltage operating condition of 4.5 V, 0.5 wt.% of alumina (Al2O3) was introduced as a ceramic filler during NCM cathode preparation. Uniformly dispersed Al2O3 over the entire area of the NCM cathodes efficiently stabilized the oxidative decomposition of the liquid electrolyte up to 5.3 V. This behavior hindered the formation of a thick surface film on the NCM cathodes after high-voltage operation (4.5 V). The Al2O3-containing NCM cathodes (NCM/Al2O3) revealed much smaller total cell resistance compared to the bare NCM cathodes, resulting in improved cycle performance and rate capabilities, which were identified as a facilitated Li+ diffusion in presence of the Al2O3 particles. NCM/Al2O3 showed a 29.4% improvement over the bare NCM (79.3 and 112.3 mAhh g−1 for bare NCM and NCM/Al2O3, respectively, after the 100th cycle) at 3C (4.3 V cutoff, C/2 for charging and 3C for discharging processes) and a 53.5% improvement (35.0 and 75.3 mAhh g−1 for NCM/Al2O3 and bare NCM, respectively) at 5C (4.5 V cutoff).