The Synergistic Effect of Ce and Y Co-Substitution on the Cycling Stability and Electrochemical Properties of A 5 B 19 -Tape Multiphase Hydrogen Storage Alloy

La–Y–Ni-based superlattice alloys are widely used as cathode materials for nickel-metal hydride (Ni-MH) batteries, but their insufficient cycling stability and electrochemical kinetics limit their development. In this work, a series of La4RNi19 (R = La, Ce, Y, Ce0.5Y0.5) superlattice alloys were synthesized using a vacuum arc furnace to systematically investigate the effects of Ce and Y substitution on the phase composition, cycling stability, and hydrogen diffusion kinetics. The results demonstrated that the substitution of Ce and Y are not only promoting the formation of the A5B19-type phase but also leading to the preferential incorporation into the [A2B4] subunit, which resulted in a significant reduction of the volume mismatch between the [A2B4] and [AB5] subunits within the 2H-A5B19 structure. The La4(Ce0.5Y0.5)Ni19 alloy exhibited a dramatic enhancement in cycling stability, with its capacity retention rate after 100 cycles soaring to 42.6%, a more than 2-fold increase from the initial 19.3%. The hydrogen diffusion coefficient (D0) was measured at 2.94 × 10–10 cm2 s–1, representing a 47.7% increase compared to the base La5Ni19 alloy. The alloy achieved a 41.12% high-rate dischargeability (HRD900) value. This attributed to the synergistic effect arising from Ce and Y co-substitution, which facilitated the in situ formation of a composite oxide layer composed of CeO2 and Y2O3. The oxygen vacancies in CeO2 provided efficient pathways for hydrogen diffusion, while the dense Y2O3 contributed to increasing the corrosion resistance. This optimized the balance between hydrogen permeability and interfacial stability. This study demonstrates that the cycling stability and the electrochemical properties of the hydrogen storage alloy can be effectively regulated by the co-substitution of bimetallic elements (Ce and Y).