Phase structure and electrochemical properties of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75−x(Fe0.43B0.57)x hydrogen storage alloys

Abstract Microstructure and electrochemical characteristics of La 0.7 Ce 0.3 Ni 3.75 Mn 0.35 Al 0.15 Cu 0.75− x (Fe 0.43 B 0.57 ) x hydrogen storage alloys have been investigated. XRD indicates that La 0.7 Ce 0.3 Ni 3.75 Mn 0.35 Al 0.15 Cu 0.75 alloy consists of a single LaNi 5 phase with CaCu 5 structure. The alloys containing FeB are composed of LaNi 5 phase with CaCu 5 structure as matrix phase and La 3 Ni 13 B 2 phase as secondary phases, and the abundance of the secondary phase gradually increases with increasing FeB content. As x increases from 0.00 to 0.20, maximum discharge capacity of the alloy electrodes monotonically decreases from 314.0 to 290.4 mAh/g. Cycling stability of the alloy electrodes increases with increasing x value. High-rate dischargeability at the discharge current density of 1200 mA/g first increases from 51.4% ( x  = 0) to 57.2% ( x  = 0.10), and then decreases to 52.7% ( x  = 0.20). The improvement in electrochemical characteristics is ascribed to the secondary phase La 3 Ni 13 B 2 , which improves the electrochemical activity of electrode surface, as well as to the phase boundary in multiphase structure, which decreases the lattice distortion and strain energy and enhances the anti-pulverization property of the alloy electrodes.