Biomedical Engineering Reference
In-Depth Information
batteries together with graphite negative electrodes. The resulting
5 V potential difference across such a cell exceeds by more than 1 V
the electrochemical stability window of the electrolyte and solvent
making the cell unstable, prone to self-discharge and to a poor cycle
life. With a high intercalation potential, TiO
is also a promising
candidate for the “5 Volts” (5 V) category electrodes.
Very recently, improvement in rate capability, capacity, and
cycling behavior has been observed in the case of nanostructured
titania, strengthening the possibility to use this oxide as a negative
material for Li-ion batteries. Bruce and Lindsay have reported
that the crystallite size and shape play key roles for improving the
performances of the electrodes [22, 23]. It also has to be noted that
their investigation concerned either hydrothermal synthesized TiO
2
2
nanotubes or anodic oxide thin films. None of these two materials is
actually organized, but they rather consist of a collection of objects
with random orientations.
In all cases, the fabrication of nanostructured electrodes
seems to be one of the most promising tracks for improving the
performances of power sources because of several advantages.
Nanomaterial-based electrodes mitigate the rate-limiting effects of
sluggish electron-kinetics and mass-transport. The large surface area
of nanomaterials serves to distribute the current density improving
electron-kinetics, while the small size ensures that intercalation
sites reside close to the surface. Furthermore, when nanomaterials
are used to assemble electrodes, new reactions mechanisms are
possible. It is proven that conversion reactions of iron oxides
work only when the oxide is nanostructured. One of the most
spectacular examples of taking the advantages of nanostructured
electrodes has been reported by Simon et al. [24]. In this approach,
electrodeposition of active negative material has been performed
onto current collectors constituted by copper nanopillars. They
have clearly demonstrated that kinetic limitations encountered
in the case of conventional electrodes can be tackled by designing
such highly nanostructured electrodes.
The properties of TiO
2
electrodes may improve dramatically
when the material is porous because of a large surface area. Due
to exciting properties offered by self-organized TiO
nanotube
2
(ntTiO
) layers such as porosity and many potential applications, the
2
Search WWH ::
Custom Search