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Advancement in storage capability and hydrogen kinetics of hydride storage alloys through nanocoating with multifunctional hybrid polymer

Final Report Summary - HYDRONANOPOL (Advancement in storage capability and hydrogen kinetics of hydride storage alloys through nanocoating with multifunctional hybrid polymer)

The market for electrical storage batteries is a global battlefield, in which European manufacturers are falling behind Far Eastern suppliers. Development of the technology for higher capacity nickel-metal hydride (NiMH) batteries could help to redress this balance by providing more ecologically benign replacements for NiCd types in such high-current density applications as power tools, hybrid vehicles and small portable devices.

Large gains in the current storage capacity of NiMH batteries can be achieved by reducing the size of the active particles form a few hundreds of microns down to the nanometre range - and thus increasing the surface / volume ratio. However, the high surface energy of such extremely small particles makes them extremely flammable in contact with air, which is very difficult to manage in production processes.

The consortium of the HYDONANOPOL project explored the application of polymeric nano-coatings as a solution to this problem. This entailed studying the behaviour of suitable polymers in terms of their ability to prevent combustion without impairing the ion conductivity of the dispersed nanoparticles. In addition, it required the development of novel multifunctional hydride storage alloys for the negative electrodes of the batteries. These were assessed for electrochemical connection efficiency and stability in the alkaline medium.

It was shown that Ormocer (registered trademark) does not affect charge transfer kinetics, nor does it influence double layer capacitance. However, in order to eliminate small losses in the hydrogen storage capacity of milled and coated materials, (probably because of electrical insulation of some particles by the polymer), optimisation of the Ormocer (registered trademark) coating is still being pursued.

Low energy milling was found to facilitate activation of the materials, but accelerated self-discharging requires further investigation and remedying. Refinement of the small-particle preparation procedure is also being undertaken to compensate for a less-than-expected improvement in the hydrogen diffusion rate for milled samples, compared with un-milled particles.