Will hydride-ion conduction power next-generation batteries?
Genki Kobayashi and Ryoji Kanno at Tokyo Institute of Technology with colleagues from the Institute for Molecular Science, Japan Science and Technology Agency, Tokyo Institute of Technology, Kyoto University and High Energy Accelerator Research Organization (KEK) in Japan have postulated that hydride ions (H-) may be useful for high-energy-density storage devices. Using an oxyhydride solid state cell the researchers have demonstrated pure H- conduction in an oxide for the first time.
Metal hydrides tend to have an inflexible lattice, which makes H– transport difficult which is why the researchers turned to oxyhydrides where oxygen and hydrogen share the same lattice sites. Another challenge is the high electron-donating properties of H-, which means that the electrons will dissociate from the H- to produce protons and electrons, giving rise to electron rather than hydride-ion transport. As a result the research team sought a system containing cations that were more electron-donating than the H-.
Crystal structure of La2-x-ySrx+yLiH1-x+yO3-y (x = 0, y = 0, 1, 2)
The researchers, who examined how the structure of their oxyhydride compounds changed with composition and synthesis conditions, also studied characteristics of the electronic structure that suggested an ionic Li-H bond in the compound, namely the existence of H– in the oxides.
All-solid-state hydride-ion cell.
A discharge curve for a solid-state battery with the Ti/o-La2LiHO3/TiH2 structure. The inset shows an illustration of the cell and the proposed electrochemical reaction.
The researchers then used La2LiHO3 in an orthorhombic structural phase (o- La2LiHO3) as an electrolyte in a cell with titanium anode and titanium hydride cathodes. Phase changes at the electrodes by the discharge were consistent with a Ti-H phase diagram suggesting hydride-ion transport. The researchers concluded: “The present success in the construction of an all-solid-state electrochemical cell exhibiting H– diffusion confirms not only the capability of the oxyhydride to act as an H– solid electrolyte but also the possibility of developing electrochemical solid devices based on H– conduction.”
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