Intrinsic/Extrinsic Degradation of Ti-V-Based Hydrogen Storage Electrode Alloys upon Cycling

The capacity degradation mechanism of the Ti-V-based hydrogen storage electrode alloys was systematically investigated from the viewpoint of intrinsic/extrinsic degradation for the first time. The oxidation/corrosion of the active components and the appearance of the irreversible hydrogen were found to be the two dominating intrinsic factors for the cycling capacity degradation of the Ti-V-based electrode alloys, rather than the segregation and dissolution of the main hydrogen absorbing element V, the loss of which had some effect on the degradation of its discharge capacity but not dominating. The extrinsic degradation of the electrode alloys was mainly caused by the pulverization of the alloy particles, the increase of the contact resistance between particles, and the reaction resistance on surfaces during charge/discharge cycling. In the meantime the pulverization of the alloy particles accelerates the oxidation/corrosion of the active components, which further promotes the formation of the oxide layer and decreases the reaction speed. The decay of the apparent discharge capacity of the Ti-V-based electrode alloys is jointly affected by these factors.