With the demand for lithium-ion batteries with high energy density on the rise, Li-excess layered oxide cathode (LLC) materials that can express higher capacity than conventional ternary cathode materials are garnering attention. Although LLC can theoretically have high capacity of 250 mAh/g or more, high discharge capacity cannot be sufficiently delivered due to the Li ion concentration gradient formed by intrinsically low Li-ion diffusivity. In this study, the Li ion concentration gradient was alleviated by reducing the primary particle size and simultaneously forming a lithium sulfate coating layer to mitigate the occurrence of unwanted surface reactions through a solution-based precursor coating process. Results showed that the average primary particle size reduced to about 167 nm. Through GITT measurement, it was confirmed that the degree of overvoltage at the end of discharge was reduced as the Li-ion concentration gradient was alleviated. In fact, high discharge capacity of 264 mAh/g was delivered at the first cycle. It was also confirmed through XPS and STEM analysis results that the lithium sulfate coating layer effectively inhibited unwanted surface reactions such as transition metal dissolution and phase transformation of the layered structure. All in all, a Li-excess layered oxide cathode material with high capacity and excellent cycle stability was synthesized.