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The loading levels of electrodes are one of the crucial parameters of high energy lithium-ion batteries (LIBs); however, their effects on specific energy and energy density remain insufficiently studied. Moreover, the rate capability can differ greatly with varying loading levels and hence requires further investigation. Herein, we investigated the relationship between electrode loading levels and electrochemical performance of LIBs via galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). We found that the differences in performance stem from differing internal resistances at varying loading levels. On one hand, internal resistance decreased with a higher number of parallel connection; on the other hand, it increased with extension of electrical pathways. As a result, the optimal loading level of commercial LiNi0.6Co0.2Mn0.2O2 cathode materials was approximately 20 mg/cm2, which corresponds to an areal capacity of 3.3 mAh/cm2. These findings will assist in the further optimization of commercially available LIBs.