Electrochemical and Kinetic Properties of La-Ce-Ni-based High-temperature Hydrogen Storage Alloys with Fe-Co Synergistic Doping

抄録

To address the performance deterioration of LaNi₅-based hydrogen storage alloys used as negative electrode materials in Ni-MH batteries under high-temperature conditions, a dual-atom modulation approach utilizing Fe-Co synergistic doping was implemented in this study. A graded series of alloys with the composition La_0.80Ce_0.20Ni_3.63Mn_0.35Al_0.27Co_0.75−xFe_x (x = 0, 0.15, 0.35, 0.55, 0.75) was synthesized via vacuum arc melting, followed by homogenization and annealing treatments. The structural evolution patterns of the alloys were examined, and the electrochemical and kinetic performance of the electrodes at three different temperatures (25 °C, 45 °C, and 65 °C) was comprehensively studied. The results revealed that Fe-Co synergistic doping preserved the hexagonal CaCu₅-type crystal structure (space group P6/mmm) of the LaNi₅-based alloys. As the Fe content increased, lattice expansion was observed. For the composition with x = 0.75, the lattice parameters increased from a = 5.041 Å to 5.061 Å and c = 4.047 Å to 4.069 Å, accompanied by a unit cell volume expansion of 1.31 %. At an elevated temperature of 65 °C, the alloy with x = 0.35 exhibited well-balanced overall properties: a discharge capacity of 327.1 mAh g⁻¹ was achieved at 60 mA g⁻¹, representing an increase of 2.8 % compared to the pure Co alloy (x = 0). After 200 cycles at 300 mA g⁻¹, it maintained a capacity retention of 59.6 %, with a high-temperature recovery (HTR) capability of 60.83 %. The incorporation of Fe has been shown to optimise hydrogen diffusion behaviour, thereby increasing the hydrogen diffusion coefficient (D₀) to 7.4 × 10⁻¹⁰ cm² s⁻¹. This represents a 34.5 % improvement in comparison to the x = 0 alloy. In addition, the corrosion resistance of the electrode surface is enhanced. The high-temperature electrode corrosion and the oxygen evolution side reaction were mitigated effectively. This study identifies an optimal Fe/Co ratio range, achieving a synergistic optimisation of discharge capacity, cycle life, and cost control across a broad temperature range (25–65 °C), thereby providing a foundation for the application of Ni-MH batteries in high-temperature environments.