Abstract:
Lithium ion batteries are fast becoming the consumer choice for powering their
electronic devices. However, current lithium batteries energy densities are not suf-
ficiently high, and cost per kWh sufficiently low, to be widely accepted as batteries
in electric vehicles.
In order to reduce the cost and increase the energy density it may be necessary to
move away from intercalation electrode materials, that are limited by the number of
vacant lithium interstitial sites available, to conversion reaction materials that can
allow multiple electron transfer. This thesis looks to investigate the use of a non-
transition metal fluoride as a cathode material in a primary or secondary lithium
battery.
Initial results for the ball milled material show specific energy densities over 2050
Wh/kg. The initial energy density rapidly faded over a period of a few cycles due to
the structural change of the material and unwanted reactions with the electrolyte.
These were identified by investigating the mechanism of the one stage discharge and
charge profile. To further improve the cycling results nanorods were synthesised
which improved the rate capability to provide an energy density of over 1250 Wh/kg
at a discharge rate of 0.25C. The capacity over repeated cycling was also improved
but the same problems that plagued the ball milled samples were also apparent in
the nanorod samples. It was found during the initial investigation of the non-transition metal fluoride
material that it is rechargeable, but for a limited number of cycles partly due to its
poor kinetics. It has the potential to be a good rechargeable battery material but if
not can satisfactorily compete with commercial primary batteries in terms of energy
density and cost, as it is a very cheap material.
