Biomedical Engineering Reference
In-Depth Information
Moreover, for nanotubes with 900 nm length, it is observed that
the characteristic nanotube geometry is unchanged after cycling:
a tube diameter of about 80 nm, wall thickness of 20 nm (top
view), and nanotube length of 920 nm (cross-sectional view). The
chemical analysis carried out using energy dispersive X-ray (EDX)
spectroscopy (not shown) reveals that there are phosphorus and
fluorine impurities. These analyses demonstrate the robustness of
the nanotube morphology, which survives after repeated cycling.
However, doing a more extended study of the whole area of the
electrodes, we found parts where there are some partially opened
nanotubes; it is also possible to see some closed nanotubes
(Fig. 5.19).
5.6 CONCLUSIONS
nanotubes are key materials for the negative
electrode of a new generation of Li-ion Batteries. Working voltages
well above graphite avoid lithium electrodeposition and extended
SEI layer formation. Short lithium diffusion and electron conducting
distances improve rate performance and an efficient capacity usage.
The materials are apt for miniaturization and use in advanced NEMS.
No toxicity and environmental friendliness are additional positive
features of these materials.
Eventually, self-organized TiO
Self-organized TiO
2
nanotubes can be easily
obtained by a powder-free fabrication method based on the
electrochemical anodization of titanium foil or titanium sputtered
onto a silicon substrate. The TiO
2
nanotubes prepared onto Si
substrate had an inner diameter between 50 and 200 nm and
about 600 nm length. This method ensures good electrical contact
between titania nanotube layers and the current collector. Also, the
resulting array shows a special mechanical stability and buffers
possible volume changes arising from the structural tetragonal-
orthorhombic conversion of anatase, or possible expansion on
insertion in amorphous titania. Using Ti foils, it is possible to obtain
nanotubes with 600 and 900 nm of thickness (or length) exhibiting
the same diameter and wall thickness. The powder-free fabrication
method used to prepare the active material directly on the current
2
Search WWH ::
Custom Search