Effects of fluorination of AB 2-type alloys and of mixing with AB 5-type alloys on the charge–discharge characteristics

Abstract

The effects of fluorination (F-treatment) of AB 2-type Laves-phase Zr 0.9Ti 0.1V 0.2Mn 0.6Co 0.1Ni 1.1 (AB 2) alloys and of mixing with untreated AB 5-type MmNi 3.68Co 0.78Mn 0.36Al 0.28 (AB 5) alloys on their charge–discharge characteristics were investigated. The F-treatment of the AB 2 alloy greatly increased initial activation rate and discharge capacity and slightly improved high-rate dischargeability. The mixing of the F-treated AB 2 alloy with untreated AB 5 (<25 μm) alloy decreased somewhat the maximum discharge capacity compared to the fluorinated AB 2 alloy but it greatly improved the high-rate dischargeability. In particular, the high-rate dischargeability for the AB 2(F)AB 5 (<25 μm) mixture positively deviated from the estimated values based on the maximum discharge capacity for both alloys and their content, suggesting that the AB 5 alloy can work as a catalyst for dehydriding the AB 2 alloy hydride besides as a hydrogen reservoir; a synergistic effect appeared by the mixing.