Phase Structure and Electrochemical Characteristics of Rhombohedral Super-Stacking La0.77Mg0.23Ni3.72 Hydrogen Storage Alloy. Issue 10 (1st January 2015)

• Record Type: Journal Article
• Authors: Du, Wenkai; Cao, Shengbiao; Li, Yuan; Zhang, Lu; Zhao, Yumeng; Yang, Shuqin; Han, Shumin
• Is Part Of: Journal of the Electrochemical Society. Volume 162:Issue 10(2015)
• Page Start: A2180
• Page End: A2187
• Publication Date: 2015-01-01
• Subjects: Crystal transformation -- Electrochemical property -- Hydrogen storage alloy -- La-Mg-Ni-based alloy -- Rhombohedral structure; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0851510jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : In recent years, ternary La–Mg–Ni-based hydrogen storage alloys have attracted attention as promising electrode materials for nickel-metal hydride batteries. A La0.77 Mg0.23 Ni3.72 alloy with the both rhombohedral (3R) Gd2 Co7 -type and Ce5 Co19 -type phases was successfully prepared by induction melting followed by annealing treatment method at 950°C. Via annealing treatment for 54 h, the CaCu5 -type, Ce2 Ni7 -type, Gd2 Co7 -type, and Ce5 Co19 -type phases of the as-cast alloy converted into the rhombohedral Gd2 Co7 -type and Ce5 Co19 -type phases. The electrochemical properties of the rhombohedral-phases alloy electrode exhibited an excellent maximum discharge capacity (388.8 mAh g −1 ) and high rate discharge ability (53.1% at a 1440 mA g −1 discharge current density). The discharge capacity retention at the 100 th cycle is particularly heightened to 86.2%. X-ray diffraction and scanning electron microscope analyses verify that the annealed alloy comprised of rhombohedral-phases exhibits a larger crystallite size and smaller strain after 100 th charge/discharge cycles than those of the alloys comprised of a mixture of hexagonal and rhombohedra polymorphic phases. Moreover, the corrosion current density of the alloy is reduced (23.53 mA cm −2 ) in an alkaline electrolyte. The superior properties of the alloy may be attributed to the R -3m space group Gd2 Co7 -type and Ce5 Co19 -type phases possessing high structural matching.