NANOSTRUCTURED TiO2 MATERIALS FOR NEW-GENERATION Li-ION BATTERIES - Electrochemical Nanofabrication: Principles and Applications - page 202

(JCPDS file 21-1272), respectively. On the other hand, the Ti layer
deposed on Si substrate was identified as hexagonally close-packed
α

nanotubes obtained
at room temperature are X-ray amorphous. On heating we observe
again the partial crystallization of titania to anatase (Fig. 5.9c).
Peaks of Ti are still present after growing the ntTiO
2

-Ti (JCPDS file no.: 44-1294) and the ntTiO

2

not only onto

μ

Ti foils but also onto Si because a layer of Ti (1.25 m in thickness)

remains after anodization (see SEM image in reference [34]). In the
particular case of the silicon substrate, 35% of the initial Ti layer is
converted into ntTiO
2

. This remaining Ti layer is not electroactive
versus lithium, as it is discussed later.

(a) (b)

Figure 5.8 nanotube layers after anodization (20 V, 20

min) in a fluoride-containing electrolyte: (a) top view, and (b) cross section
of the amorphous TiO

SEM images of TiO

2

nanotube layers onto Si Substrate.

2

The robustness of the two substrates should be addressed
considering its integrity under these annealing conditions since
no differences were observed by XRD and SEM. Moreover, the
microstructure of the nanotubes remains basically unmodified as
it can be seen from the SEM image given in Fig. 5.9. It is clear that
no morphological changes appear in the porous structure after
this thermal treatment, which is in agreement with previous data
reported by Schmuki's group [42].
The thickness of nanotubes can be estimated from Eq. 5.1 and
using Faraday's law:

QM



L

, (5.3)

F n δ