Understanding the degradation mechanism of Lithium-ion batteries (LIBs) is critical in developing high-performance LIBs, and the investigation of their electrical conductivity evolution during cycling can lead to a better understanding of the degradation mechanism of the cathode materials for Li-ion batteries (LIBs). Here, we studied the evolution of the electrical conductivity of LiNi0.8Co0.15Al0.05O2 (NCA) particles for LIB cathodes using scanning spreading resistance microscopy (SSRM). After 300 charge/discharge cycles, stepwise-increasing resistance distributions toward the centers of the secondary particles are observed. These distributions correspond to the degenerated granular structures of the secondary particles caused by the formation of microcracks. In addition, the correlation between the electrical conductivity and microstructure of the NCA cathode is established to explain the observed decay of the NCA discharge capacity. Our findings can provide an insight into the debatable degradation mechanism of LIB cathode materials such as NCA and NMC (LiNixMnyCozO2, x + y + z = 1).