Phase and Lattice Adjustment via Ti Content Regulation in AB‐Type Ti–Fe–Mn Alloys for Optimized Activation and Cycling Stability

How to optimize activation and enhance cycle life is a crucial part in promoting large-scale stationary applications of AB-type TiFe-based hydrogen storage alloys. In this study, the phase composition and lattice size are manipulated and the correlation with activation and cycling stability is investigated by varying the Ti content. It is elaborated that the amorphous passive film on the alloy surface, predominantly composed of TiO₂, exerts a decisive influence on the ease of activation, the increase in Ti content leads to the thickening of the passivation film, which significantly prolongs the activation latency from 200 s to 1750 s, and the first-principles calculation based on density functional theory reveals that the C14 Laves phase is a favorable window for hydrogen atom diffusion. More crucially, the increase in Ti content expands the lattice constant of the TiFe phase from 2.9820 Å to 3.0022 Å, the expanded TiFe lattice generates reduced strain during cycling, resulting in smaller post-cycling lattice expansion. The enlarged lattice structure enhances structural stability, leading to improved capacity retention from 92% to 96% after 50 cycles. Remarkably, the Ti₅₃(Fe_0.8Mn_0.2)₄₇ alloy demonstrates excellent comprehensive properties, including easy activation, large capacity, and high cycling stability.