Composite hydride electrode materials

Abstract

A new class of electrode materials — composite hydride materials — is proposed for anodes in hydride-based rechargeable batteries. The composites were synthesized by mechanical mixing of two components: a major component having good hydrogen storage properties and a minor component used as surface activator. The major component was selected among nonconventional or conventional hydride electrode materials; alloys and intermetallic compounds of the AB 2 or AB 5 type. The minor component was amorphous Mg x Ni 1− x ( x=0.4, 0.5) or a 1:1 mixture of Mg x Ni 1− x and LmM 5 (where Lm is a La-rich mischmetal and M 5 is Ni 3.6Co 0.8Mn 0.3Al 0.3). The role of the minor component was to improve the kinetics of electrochemical charging and to eliminate the initial activation of the major component. Experimental results have shown that the electrodes manufactured from composite materials have the following advantages: (1) elimination of the initial activation; (2) a significant improvement of electrode kinetics, resulting in better rate capabilities and higher charging efficiency; (3) a drop of the charging overpotential, resulting in better energy efficiency of the battery; (4) better cycling behavior; (5) in most cases, a considerable increase of the discharge capacity with respect to that of the major component.