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

Microstructure and electrochemical characteristics of La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75−x(Fe0.43B0.57)x hydrogen storage alloys have been investigated. XRD indicates that La0.7Ce0.3Ni3.75Mn0.35Al0.15Cu0.75 alloy consists of a single LaNi5 phase with CaCu5 structure. The alloys containing FeB are composed of LaNi5 phase with CaCu5 structure as matrix phase and La3Ni13B2 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 La3Ni13B2, 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.

► Commercial Fe–B alloy has lower cost than Cu, pure Fe and B, and lower melt point than pure Fe and B.
► Alloys consist of LaNi5 phase and La3Ni13B2 phase, and La3Ni13B2 phase increases with increasing x.
► The alloy with x = 0.10 exhibits the best high-rate dischargeability.
► Cycling stability of alloy electrodes increases with increasing x value.
► The improvement of HRD and cycling stability is ascribed to La3Ni13B2 phase and phase boundary.