Significance of First Cycle in Electrochemical Characterization of Co-Zn Doped LiNi1-x-y-0.02CoxZnyMg0.02O2 Cathodes for LIBs

• The research focused on analyzing the first-cycle electrochemical performance and structural stability of nickel-rich cathode materials by doping with cobalt and zinc. • Strategic doping of Co and Zn into LiNi 1-x-y-0.02 Mg 0.02 Co x Zn y O 2 aimed to leverage the beneficial properties of these elements. Increasing the Co and Zn concentrations increased the dielectric constant, and the semiconducting nature was shown by the conductivity variation (1.58×10 −5 to 8.46×10 −6 Scm −1 ). • The concentrations of Ni, Co, Zn, and Mg can vary based on the values of x and y which are the parameters that represent the fractional amounts of cobalt (Co) and zinc (Zn) substitution in the crystal lattice, respectively. • The morphology, structure, functional group, and first cycle charge-discharge, impedance analysis, ion transport analysis, and cyclic voltammetry of the produced LiNi 1-x-y-0.02 Mg 0.02 Co x Zn y O 2 (x = y = 0.0, 0.01, 0.02, 0.03, and 0.04) cathode materials have been examined and described in detail in the paper. • Safety improvements were targeted through the stabilization of the cathode structure, potentially enhancing safety by influencing the formation of a stable solid electrolyte interphase (SEI). Layer-structured cathode materials, LiNi 1-x-y-0.02 Co x Zn y Mg 0.02 O 2 (x and y from 0.0 to 0.04), were synthesized via a solid-state reaction to enhance electrochemical properties and structural stability while maintaining high capacity retention. Despite a trend to phase out Cobalt, its controlled inclusion reduces cation mixing and improves stability, which is critical in the first cycle’s performance. Characterization using Thermogravimetry Differential Thermal Analysis (TG/DTA), X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Fourier Transform Infrared (FTIR) Spectroscopy, and electrochemical testing revealed rhombohedral structures, average crystallite sizes of 1.980 to 2.710 nm (Scherrer’s formula) and 3.19–3.85 nm (Williamson-Hall plot), and grain sizes around 3.32–3.45 μm. Energy-dispersive X-ray Spectroscopy (EDS) confirmed effective Co and Zn doping. Electrochemical impedance spectroscopy (EIS) and Nyquist plot analysis showed improved conductivity and optimized ion transport, essential for rapid charge/discharge rates and stability. The first-cycle charge/discharge capacities ranged from 170.55–175.60 mAhg⁻¹ and 169.91–173.17 mAhg⁻¹, respectively, with over 85% capacity retention after subsequent cycles. The LiNi 0.92 Mg 0.02 Zn 0.03 Co 0.03 O 2 composition exhibited a peak charge current of 0.06 mA at 4.0 V and a minimum discharge current of -0.02 mA at 2.0 V, highlighting enhanced electrochemical performance. This study emphasizes the critical role of first-cycle characterization in understanding the electrochemical behavior and stability of Co, Zn, and Mg-doped layered cathodes, highlighting their potential for high-performance Li-ion batteries.