Study On Novel Anodic Materials For Zinc-Nikel Secondary Alkaline Batteries

Zinc/nickel (Zn-Ni) secondary alkaline system is a promising candidate for the new generation of green power sources used in electric vehicle (EV) or hybrid electric vehicle (HEV) in recent years. It has attractive advantages of high energy and power densities, high open circuit voltage, excellent low-temperature performance, low cost and environment friendly. However, the commercial applications of Zn-Ni alkaline secondary batteries are severely limited by their poor cycling characteristic, which mainly results from the drawbacks of zinc electrode, such as shape change, zinc dendrite formation, surface passivation, zinc self-corrosion and self-discharge. These problems derive from a high solubility of the discharge products of zinc electrode in alkaline electrolyte and non-uniform deposition of zinc active material during charging. Various attempts, such as the use of additives in either the anode or the electrolyte, the modification of Zn electrode and calcium zincate as the anodic active material, have been made to overcome the shape change and dissolution problems of the Zn electrode. Nevertheless, these approaches could not effectively overcome these obstacles. Base on these points, the present work discussed the electrochemical properties of Zn-Al-LDHs prepared by different methods as novel anodic materials for Zn-Ni secondary alkaline batteries. Besides, the In(OH)3-coated Zn-Al-LDH was successfully prepared as electrode material and the structure as well as the electrochemical performance was systematically investigated. Moreover, the Zn-Al-La-LDHs have been proposed as zinc electrode materials for the first time and the electrochemical properties were studied in details.Zn-Al-CO3layered double hydroxides were prepared by the co-precipitation and hydrothermal method. The results showed that the synthetic samples prepared by different methods have been characterized by The Fourier Transform Infrared Spectroscopy (FTIR) spectra, X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images. The Zn-Al-LDH prepared by hydrothermal method has evenly distributed sizes, well-crystallized and typical hexagonal crystal structure, which is much superior to that by the co-precipitation. As anodic materials for Zn-Ni secondary alkaline cells, the Zn-Al-LDH prepared by hydrothermal method has shown lower charge plateau, higher discharge plateau and better cycle stability.In(OH)3-coated Zn-Al-LDH is prepared by homogeneous precipitation method. The X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images reveal that the In(OH)3is successfully coated on the surface of the Zn-Al-LDH particles. And about2.5wt%of coating is determined through the energy dispersive X-ray spectrum (EDS). The electrochemical performance of In(OH)3-coated Zn-Al-Zn-Al-LDH is investigated by cyclic voltammetry (CV), electrochemical impedance spectroscope (EIS), Tafel polarization curves and galvanostatic charge-discharge measurements. The EIS exhibits a higher charge-transfer resistance and the Tafel polarization curves reveals a more positive corrosion potential for the In(OH)3-coated Zn-Al-Zn-Al-LDH, in comparison with the pristine Zn-Al-LDH and the mixture of Zn-Al-LDH and In(OH)3. After50cell cycles, the In(OH)3-coated Zn-Al-LDH retains a specific discharge capacity of364.0mAh·g-1with a retention rate of96.9%.Zn-Al-La-CO3layered double hydroxides (LDHs) with different Zn/Al/La molar ratio are prepared by hydrothermal method and proposed as a novel anodic material in Zinc-Nickel secondary alkaline cells. The Fourier Transform Infrared Spectroscopy (FTIR) spectra, X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images reveal that the as-prepared samples are well-crystallized and hexagon layer structure. Electrochemical performances of Zn-Al-La-LDHs with different Zn/Al/La molar ratios are investigated by galvanostatic charge-discharge measurements, cyclic voltammograms (CV) and Tafel polarization curves. In comparison with the Zn-Al-LDH, the Zn-Al-La-LDHs with different Zn/Al/La molar ratios have more stable cycling performance. After400cell cycles, the Zn-Al-La-LDH with Zn:Al:La=3:0.8:0.2retains specific discharge capacity of297mAh·g-1with a retention rate of79.0%, which is much superior to that of 205mAh·g-1with a retention rate of53.5%for the Zn-Al-La-LDH with Zn:Al:La=3:0.9:0.1and241mAh·g-1with a retention rate of69.0%for the Zn-Al-La-LDH with Zn:Al:La=3:0.6:0.4. The results demonstrate that the Zn-Al-La-LDH with Zn:Al:La=3:0.8:0.2has the best reversible cycling behavior. The CV exhibits well reversibility and the Tafel polarization curves reveals a more positive corrosion potential for Zn-Al-La-hydrotalcite.