Li-ion batteries power our modern mobile world. They are the cornerstone of the electric vehicle, a market whose growth is accelerating rapidly; and the mobile phone, which encompasses billions of devices used by most people on the planet. The cathode material of Li-ion batteries is the limiting factor of battery capacity, as well as one of the culprits of battery failure and thus improving this material is critical to realize better performing batteries. The layered metal oxide LiNi_xMn_yCo_zO₂ is the current market-leader in the cathode space. Many compositions are in use with the industry pushing capacity higher with high-Ni compositions. However, high-Ni compositions come at the cost of material stability, i.e., battery lifetime. To stabilize the cathode, many metals have been substituted into the material to resist structural transformations and to prevent surface reactions with the electrolyte. Of the substituted metals, aluminum has been explored extensively. However, most studies are limited to a few key compositions of NMC and a systematic study of the structural and electrochemical impact of Al substitution has not been completed on the full range of NMC compositions. In this work, the effects of different levels of aluminum substitution are investigated and, in total, 320 different compositions are explored using high-throughput techniques. X-ray diffraction is used to understand the structures at all compositions and combinatorial electrochemistry is performed to extract important battery metrics related to energy density, cycling performance, and irreversible capacity. This work provides insight into how accommodating different NMC compositions are to aluminum substitution and the effects of the substitutions on their electrochemistry.