In this study, Li[NixCoyMnz]O2 cathode composition library was fabricated using combinatorial methodology and characterized using nanoindentation to create a mechanical properties database as a function of Li[NixCoyMnz]O2 composition. A single sputter deposition from LiCoO2, LiNiO2, and LiMn2O4 compound targets resulted in a composition range of 3–44 at.% Co, 20–80 at.% Ni, and 5–50 at.% Mn. Young’s modulus and hardness values were evaluated before and after charge–discharge cycles, and a strong dependency of the mechanical properties on composition was found; Mn-rich composition showed highest retention of its mechanical properties whereas the properties degraded more significantly for the Ni-rich composition. Electrochemical performance was analyzed and compared to mechanical properties at various Li[NixCoyMnz]O2 compositions and a strong correlation between enhanced mechanical properties retention leading to superior discharge capacity retention was found for the Mn-rich compositions. Li[Ni0.33Co0.30Mn0.34]O2 composition showed optimized electrochemical and mechanical properties, where it retained 38% and 50% of its Young’s modulus and hardness after cycling while demonstrating 91% discharge capacity retention after 20 cycles at 1 C-rate.