<p>This study investigates the impact of substituting cobalt (Co) with nickel (Ni) in lithium-ion battery (LIB) cathode materials. X-ray diffraction (XRD) analysis reveals changes in peak positions and intensities due to Ni substitution, suggesting lattice parameter variations and potential effects on electrochemical stability and charge/discharge rates. Crystallite size calculations indicate that LiNiO₂ has a more stable structure, while LiCo_0.5Ni_0.5O₂ exhibits increased cation disorder. SEM and FTIR analyses confirm structural differences, with Ni substitution influencing particle morphology and vibrational properties. The study concludes that LiCo_0.5Ni_0.5O₂ offers an optimal balance of structural stability, capacity, and lithium-ion mobility, making it well-suited for high-energy–density LIB applications, including electric vehicles and grid storage. Additionally, this study evaluates the impact of nickel (Ni) substitution for cobalt (Co) in lithium-ion battery (LIB) cathode materials by analyzing impedance characteristics. The real part of impedance (Z1) shows a decreasing trend with increasing frequency, with LiCo_0.5Ni_0.5O₂ exhibiting the lowest initial impedance, indicating superior conductivity. The imaginary part (Z2) initially peaks for LiCo_0.5Ni_0.5O₂ but sharply decreases, suggesting enhanced charge transfer properties at higher frequencies. The Cole–Cole diagram further illustrates that LiCo_0.5Ni_0.5O₂ has the least charge transfer resistance, promoting faster charge/discharge cycles. The loss tangent (tanδ) analysis indicates minimal energy dissipation at high frequencies, reinforcing the material’s suitability for energy storage. Overall, LiCo_0.5Ni_0.5O₂ demonstrates the optimal balance of conductivity, stability, and efficiency, making it the best candidate for high-performance LIB applications.</p>