Hydrogen storage and capacity degradation mechanism of superlattice La-Y-Ni-based hydrogen storage alloy

New La-Y-Ni-based hydrogen storage alloys exhibit key technological advantages for energy storage; however, several challenges arise because of their insufficient cycle life. In this study, we design a non-stoichiometric structure and present a scheme for obtaining a stable superlattice structure by optimizing multi-component elements and understanding the structural evolution and anti-degradation mechanism for increasing the cycle life. The rationality of the scheme is verified by designing AB3.67-type La1.4Ce0.5Y4.1-xSmxNi20Mn1.2Al0.8 (x = 0, 0.2, 0.3, and 0.4) alloys. Substituting Y with an appropriate amount of Sm reduces capacity degradationin both in electrochemistry and solid/H2 reactions because it effectively inhibits the transition of the stable phase and this regulation reduces the mismatch of subunits in the Gd2Co7-type phase, especially the control [A2B4] subunit instead of the [AB5] subunit. Further, a capacity degradation mechanism is illustrated and the entire process is divided into three stages. The corrosion resistance of synergistic elements in the first stage (<100 cycles) of the electrochemical reaction is a decisive factor controlling the long-term cyclic stability of alloys. Although the amorphous phase in the solid-H2 reaction is the main factor responsible for decay, the La1.4Ce0.5Y3.8Sm0.3Ni20Mn1.2Al0.8 alloy shows better electrochemical properties, with a maximum discharge capacity, H2-absorption capacity, and capacity retention rate S100 of 377.7 mAh g−1, 1.64 wt%, and 90.9 %, respectively. After 500 cycles, the capacity retention rate is enhanced from 42 % to 60.9 %. The proposed scheme is expected to prom.