Effect of Sn substitution for Co on microstructure and electrochemical performance of AB5 type La0.7Mg0.3Al0.3Mn0.4Co0.5-xSnxNi3.8 (x=0-0.5) alloys
(1. Institute for Semiconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia;
2. Materials Science and Technology Center, Nuclear and Energy Research Institute,
University of S？o Paulo, SP 05508-900, Brazil)
2. Materials Science and Technology Center, Nuclear and Energy Research Institute,
University of S？o Paulo, SP 05508-900, Brazil)
Abstract: The effects of substitution of Sn for Co on the microstructure, hydrogen storage and electrochemical discharge capacity of La0.7Mg0.3Al0.3Mn0.4Co0.5-xSnxNi3.8 (x=0, 0.1, 0.2, 0.3 and 0.5) alloys were investigated using X-ray diffraction (XRD), pressure composition isotherm (PCT) and electrochemical discharge cycle. XRD, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) tests showed that all of alloys are mainly composed of LaNi5 and MgNi2 phases, but when increasing the content of Sn in alloys, the LaNiSn phase appears and microstructure is refined. The PCT showed that increasing substitution of Sn for Co results in decrease of the maximum hydrogen storage capacity from 1.48% (x=0) to 0.85% (x=0.5). The electrochemical tests indicated that the maximum discharge capacity decreases from 337.1 mA？h/g (x=0) to 239.8 mA？h/g (x=0.5); however, the discharge capacity retention at the 100th cycle increases from 70.2% (x=0) to 78.0% (x=0.5).
Key words: hydrogen storage alloys; microstructure; Ni-MH batteries; Sn; Co; substitution