Synthesis, characterization, and electrochemical performance of novel Zn_xCd_1-xO compounds as negative electrodes in lithium batteries

Cadmium and zinc oxide compounds of chemical formula Zn_xCd_1-xO, where x = 0–1 with various weight ratios, were synthesized by hydrothermal technique. These compounds are used as novel anode materials in lithium batteries. The crystal structure was investigated by X-ray diffraction (XRD). The crystal structure of ZnO is hexagonal like wurtzite, while the crystal structure of CdO is cubic. The morphology of samples was investigated by field emission scanning electron microscope (FESEM). The morphology of pure CdO is like bacillary, whereas ZnO has spheroid morphology. The Zn_0.4Cd_0.6O sample reveals a coral reef-like structure. X-ray photoelectron spectroscopy (XPS) explained binding energy, chemical composition, and elemental states of ZnO, CdO, and the mixed oxides. The prepared compounds were applied as anode active materials in the collected CR2032 coin cell versus the Li metal. The cyclic voltammetry (CV) studies revealed three cathodic peaks at 1.10, 0.5, and 0.15 V vs. Li⁺, respectively, with ZnO, Zn_0.8Cd_0.2O, and Zn_0.4Cd_0.6O cells. These peaks are for solid electrolyte interface (SEI) formation and lithiation (discharging) processes. On the other hand, there are three main apparent anodic peaks at 0.01, 0.20, and 1.10 V, respectively for delithiation (charging) reactions. Galvanostatic measurements were carried out. Zn_0.4Cd_0.6O cell exhibited the maximum specific capacity of 1213 mAhg⁻¹ for the first discharge process and delivered a capacity of 800 mAhg⁻¹ for cycle life up to 100 cycles. Also, the electrochemical impedance spectroscopy (EIS) measurements demonstrated a reasonable value of charge transfer resistance (R_ct ~ 80.2 Ω) for the Zn_0.4Cd_0.6O cell, which is close to that of pure ZnO (68 Ω). Therefore, Zn_xCd_1-xO materials are good candidates for use as anode electrodes in lithium batteries.