Ionic conductors for solid state battery systems.
In this projeot, it has been demonstrated that ouprous iodide -
sulphonium iodide double salts, similar to the silver iodide systems
previously studied by other workers, are sui table for use in ambient
temperatuI9 batteries for low cuzrerre applications.
A number of potential solid electrolytes, in which the mobile speoies
is oaloium, have also been investigated, and areas for further work have
been defined. The I9lavent seotion of the thesis is confidential as
patent proceedings a~ possible.
. The project has involved not only a search for new electrolytes, but
also the development of a search strategy. In view of the limitations of
di rect conductivity measurements on compaoted materials, arising from
electrioal contact probl~ms, ConsidllJrable use has been made of Lndirac t
methods. A critical ~view of standard electroohemical techniques, often
adapted from aqueous methods, has been oarried out. This has highlighted
shortcomings in the measurements of such parameters as electronic
conductivi ty, where the self-discharge rate, a parameter used by battery
technologists, has been found more meaningful than the results obtained
fran l-/agners blocking eleotrode teohn1que.
X-ray diffraction (XRD), and differential thermal analysiS (MA) have
been used to disprove the commonassertion that the effect of addition of
organio dopant materials to silver iodide has the effeot of stabilizing
the high temperature high conductivity alpha phase.
CuI based eleotrolytes have been found to differ significantly from
the AgI analogues in several respects. No simple structural cri terion,
such as the Group Weighting Coefficient for AgI systems, could be found
to prediot the effect of addition of organic sulphonium iodide dopants.
Battery cells based on CuI did not give the expected the rmodvnnmi o
open circuit voltap:e (OCV), and three electrode meaauremen t a failed to
elucidate this anomaly. The possible involvement of the cupric ion was
explored in several ways, including the first application of Auger
electron spectroscopy for this type of electrolyte system.
The battery discharge characteristics showed a fairly low efficiency,
but indirect evidence including the inadvertent involvement of a novel
solid state aurous system, pointed to the majority of the anode material
being unavailable for reaction.