High energy density strategies: from hydride-forming materials research to battery integration

Two different strategies are outlined to develop both high energy density and space-efficient batteries, including the most widely applied rechargeable nickel-metal hydride (NiMH) and Li-ion batteries. The hydrogen storage capacity of fluorite-structured Mg-containing compounds are shown to have a reversible electrochemical storage capacity of more than four times that of the commonly used MischMetal-based AB5 compounds in NiMH, i.e. 1500 mAh/g (5.6 wt.%). The formation of octahedral sites within the crystal lattice is argued to be very crucial for the improved kinetics of hydrogen absorption and desorption. It is shown that the fluorite-structure can be conserved with both precious Sc and the less expensive Ti up to a Mg content of 80 at.%. Both thermodynamic and kinetic data are presented in relation to the materials composition. In addition, the development of preshaped batteries, as the first step to battery integration, has contributed to a much higher level of design freedom for portable electronic equipment. The manufacturing process of preshaped batteries will be described together with their electrochemical characteristics. Advantageously, the mechanical stability is provided locally by polymer rivets, allowing to get rid of heavy metallic casings and to make use of a much wider range of battery shapes.