Comparative study on the capacity degradation behavior of Pr5Co19-type single-phase Pr4MgNi19 and La4MgNi19 alloys

Abstract Pr 5 Co 19 -type single-phase Pr 4 MgNi 19 and La 4 MgNi 19 alloys are prepared by powder sintering, and the capacity degradation behavior of the two alloys is investigated. The Pr 4 MgNi 19 and La 4 MgNi 19 alloy electrodes have similar discharge capacities but exhibit large differences in cycling stability. The capacity loss rate of Pr 4 MgNi 19 alloy electrode is 22.5% at the 200 th cycle, while that of La 4 MgNi 19 alloy electrode is 43.5%. It is found that the hydroxides on surface of La 4 MgNi 19 alloys accumulate disorderly while the hydroxides on surface of Pr 4 MgNi 19 alloys form a compact layer that protects the active material from corrosion. After 200 cycles, the abundance of Pr(OH) 3 in Pr 4 MgNi 19 alloy is 8.07 wt%, which is far less than that of La(OH) 3 in La 4 MgNi 19 alloy (24.74 wt%). Pr 4 MgNi 19 alloys not only have lower surface oxidization but also possess higher anti-pulverization ability. The abundance of the Pr 5 Co 19 -type phase in Pr 4 MgNi 19 alloy remains 80.88 wt% after 200 cycles, while that of La 4 MgNi 19 alloy is 32.01 wt%. The difference between the expansion rates of [A 2 B 4 ] and [AB 5 ] subunits in Pr 4 MgNi 19 alloy is 4.26%, which is smaller than that in La 4 MgNi 19 alloy (10.14%). The dense corrosion-resistant protective layer and lower lattice mismatch jointly contribute to the superior cycling stability of Pr 4 MgNi 19 alloy.