Abstract: Ni-rich cathode materials, such as Li[Ni1−x−yCoxMny]O2 (NCM) and Li[Ni1−x−yCoxAly]O2 (NCA), are attracting increasing attention in the automobile industry owing to their high reversible capacities and high operating voltages (up to 3.6 V vs. Li/Li+). In this study, a simple dry doping method was employed to fabricate a quaternary Ni-rich cathode material Li(Ni0.9Co0.06Mn0.04)1−xAlxO2 (NCMA, 0 ≤ x ≤ 0.065), wherein inactive Al was doped to improve the electrochemical performance and thermal stability of the base material, NCM. Although Al decreased the capacity and initial efficiency of the material owing to its inactive nature, it enhanced the rate performance by increasing the spacing of the Li slabs as well as the structural stability to improve the cycling performance and thermal stability. The capacity retention of Li(Ni0.9Co0.06Mn0.04)0.95Al0.050O2 increased to 95.04% (3.0–4.3 V, 0.5 C, 25 ℃) and 94.21% (3.0–4.3 V, 0.5 C, 45 ℃) after 100 cycles.