Biomedical Engineering Reference
In-Depth Information
layers
formed onto Si are attributed to the nature of Ti thin film. Compared
with ntTiO
Therefore, the better capacities obtained from ntTiO
2
layers grown from mechanically polished Ti foils,
anodization of titanium thin film obtained by physical vapor
deposition (PVD) process leads to the formation of highly flat ntTiO
2
2
layer. Thus, we assume that the contact between the ntTiO
layers
2
and the electrolyte is drastically improved.
Now we describe the electrochemical behavior of ntTiO
2
grown
on Ti foils for 4 h at 20 V, which resulted in about 900 nm of length.
For the purpose of comparing its electrochemical performance
with other thin films described in literature, we show the data in
Table 5.2. Table 5.2 presents a comparison of nanotubes versus the
compact oxide layer to really compare the nanotube morphology
exhibit improved electrochemical behavior in lithium cell. Figure
5.15a,b shows the galvanostatic discharge/charge curves versus the
composition of the as-formed ntTiO
2
-based electrode cycled between
2.6 and 1.0 V at a rate of 20 μA cm
(C/2). During the first discharge
(lithium insertion), the voltage plateau at 1.72 V corresponding to
lithium insertion into crystalline TiO
2
-
2
is not present. Only one pseudo
plateau at about 1.15 V contributes to a large irreversible reaction of
Li. A total capacity of 105 μAh cm
is measured at the end of the first
discharge with a reversible capacity of 50 μAh cm
-
2
-
2
, leading to an
irreversible capacity of 55 μAh cm
-
2
. After 50 cycles, the as-prepared
. Nevertheless,
the overlapping of the quasi-plateaus in galvanostatic curves often
hinders a clear resolution of these processes. For this purpose, the
derivative curves were calculated and plotted (Fig. 5.15c,d). Now
the horizontal quasi-plateaus become resolved bands. Derivative
curves of the as-formed ntTiO
2
ntTiO
layer shows a reversible capacity of 43 μAh cm
-
2
2
demonstrate clearly that the process
at 1.15 V is irreversible (Fig. 5.15c,d). Moreover, a very broad band in
the range of 2.4-1.4 V during discharge and charge is still visible on
further cycling, suggesting that the insertion/deinsertion process is
reversible. Compared with usual large anatase particles, the surface
area that the nanotube layers expose to the electrolyte is higher,
and this leads to a more facile insertion of lithium. Furthermore, the
existence of organized 1D nanotubular structures might contribute
to a homogeneous insertion process.
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