Synthesis, structural characterization, and electrochemical properties of the Mg and Mn doped-Ni(OH)2 for use as active cathode materials in NiFe batteries

Abstract

Ni(OH)2 is one of the most interesting electrode substances for high-performance nickel–iron batteries owing to its low cost, high specific capacitance, and environmental compatibility. However, the Ni(OH)2 cathode electrode exhibits poor performance due to (i) competitive reactions such as the oxidation of the active material and oxygen evolution. (ii) the reduced charge acceptance of the Ni(OH)2 positive electrode is related to a relatively long distance between the Ni(OH)2 particles and the nearest portion of the substrate. In this study, β-Ni (OH)2 is used as a starting material. Then, the Ni2+ in the compound β-Ni(OH)2 material is partially substituted with Mg2+ and Mn2+, separately, and the performance of the as-prepared materials was optimized and examined. XRD, FTIR, TG-DTA, SEM/EDS, and ICP-OES confirmed the formation of the expected compositions. The Ni0.95Mg0.05(OH)2 and Ni0.9Mn0.1(OH)2 based-samples were optimal compositions with promising electrochemical activities. The partial substitution of Mg2+ allowed separation of anodic/cathodic peaks and oxygen evolution. For example, the anodic and cathodic peaks are easier to identify because their potential shifted to more negative potentials. When using three-electrode configurations, the un-doped Ni(OH)2 electrode discharge capacity showed a reduction of 76% after the 100th cycle. In contrast, the Ni0.95Mg0.05(OH)2 and Ni0.9Mn0.1(OH)2 electrode demonstrated a reduction of only 15% and 12% in discharge capacities after 100th cycles, respectively. When using a two-electrode configuration, the obtained discharge capacities were 40 mAh/g for the un-doped Ni(OH)2 electrode, 120 mAh/g for the i0.95Mg0.05(OH)2 electrode, and 159 mAh/ g for the Ni0.9Mn0.1(OH)2 electrode with an electrode cycle life of 43.49%, 88.24%, 88.54%, respectively.