Biomedical Engineering Reference
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per cycle leads to a cycling efficiency of 71%. Although lower values
of specific capacity are observed using faster kinetics, the efficiency
on cycling is improved and can reach 90% in the case of crystalline
ntTiO
or 2.5 C (Fig. 5.17c). The higher
efficiency on cycling obtained with crystalline materials compared
with amorphous structures is due to the lower amount of structural
defects and Li-ion trap sites.
at a rate of 100 μA cm
-
2
2
(a)
(b)
current density: 5
µ
A cm
-2
current density: 20
µ
A cm
-2
140
140
Amorphous ntTiO
2
(900 nm)
Crystalline ntTiO
2
Amorphous ntTiO
2
(900 nm)
Crystalline ntTiO
2
120
120
100
100
80
80
60
60
40
40
20
20
0
0
0
10
20
30
40
50
0
10
20
30
40
50
Cycle Number /n
Cycle Number / n
current density: 100
µ
A cm
-2
(c)
140
Amorphous ntTiO
2
(900 nm)
Crystalline ntTiO
2
120
100
80
60
40
20
0
0
10
20
30
40
50
Cycle Number / n
Figure 5.17
Specific reversible capacity vs. cycle number in lithium cells
for the as-formed or “amorphous” (closed and colored symbols) and
annealed TiO
(open symbols) nanotube layer with 900 nm length cycled at
2
(a) 5 μA cm
-
2
(C/8), (b) 20 μA cm
-
2
(C/2), and (C) 100 μA cm
-
2
(2.5C). Note:
C/
rate means that the total capacities of the cell correspond after 1 h
in discharge.
n
layers obtained by anodization in
fluorine-containing electrolyte and whose lengths are about 600—
900 nm show enhanced electrochemical properties, we have also
fabricated two sorts of new TiO
To demonstrate that ntTiO
2
samples, and the variation in the
areal capacity vs. cycling has been studied in
(i)
2
compact layer electrochemically grown at 20 V
for 60 min in 1 M H
TiO
2
PO
4
+ 1 M NaOH electrolyte. The
3
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