Development and characterization of composite nickel electrode for nickel-iron battery based energy storage

Abstract

In this study, a β-Ni(OH)2 material was synthesized using the co-precipitation method followed by hydrothermal treatment. The effect of stirring, ageing and hydrothermal treatment step during the synthesis of the Ni(OH)2 material were evaluated. Secondly, the impact of carbon black as a conductive network for Ni(OH)2 active material was gauged. Thirdly, the effect of the partial substitution of Cu2+ for β-Ni(OH)2 material, Co2+ for β-Ni(OH)2 material, Al3+ for β-Ni(OH)2 material, Mg2+ for β-Ni(OH)2 material, Mn2+ for β-Ni(OH)2 material, was then optimised and evaluated for electrochemical performance. Four weight percentages (5 wt.%, 10 wt.%, 25 wt.%, and 50 wt.%) of additives (Cu2+, Co2+, Al3+, Mg2+, Mn2+) were partial substitutions for the β-Ni(OH)2 material. XRD, FTIR, TG-DTA, and SEM were used to measure the morphologies of the material. SEM/EDS and ICP-OES were used to confirm the composition of the material. Lastly, a novel bipolar battery cell prepared using Ni0.75Cu0.25(OH)2 as the active cathode material was evaluated for Ni-Fe battery applications. The physical characterization performed for β-Ni(OH)2 material concluded that the hydrothermal treatment step was vital for this study to produce the expected Ni(OH)2-based materials. The addition of 5 wt.%, carbon black powder improves the utilization of the active material; however, it leads to a decrease in the stability of the electrode. For example, the specific discharge capacity (after 20 cycle activation) was increased by 74% compared to 0 wt.% carbon black added to the positive nickel electrode. However, a drastic decrease in specific discharge capacity was observed after an additional 60 cycles. The specific discharge capacity of the synthesized Ni(OH)2 with 5 wt.% carbon black electrode decreased by 66%, while the synthesized Ni(OH)2 with 0 wt.% carbon black decreased by only 18% after the 80 cycles. In addition, the partial substitution of Cu2+ for β-Ni(OH)2 significantly improves the coulombic efficiency of the β-Ni(OH)2 active material. It also increases the specific discharge capacity and enhances the stability of the electrode. Lastly, a novel bipolar battery cell was prepared and evaluated its discharge capacities for the Ni-Fe battery applications. The Ni0.75Cu0.25(OH)2 material was first deposited onto both a graphite composite and Ni-mesh substrates to form the monopolar electrodes. The bipolar-based Ni-Fe battery cell demonstrated a discharge capacity of 158 mAh/g after the 100th cycle, corresponding to a coloumbic efficiency of 72%. A cost evaluation of the typical battery plant for a bipolar based Ni-Fe was estimated, and it was found that the bipolar design reduces the production cost by 33% from R12/Wh to R8/Wh.