78
6 Applications of Carbon Nanostructures Produced in Molten Salts
particles as well as the electrical disconnection between the particles and the current
collector, and thus poor cyclability [17, 18].
6.2 Metal–Carbon Nanocomposites as Anode Materials
for Li-Ion Batteries
The replacement of graphite by a metallic anode can offer benefits such as a higher
specific capacity, at least during the initial cycles, due to more lithium ions that can
contribute to the reaction scheme (6.3) compared to that of (6.1):
aMe + bLi
+
+ be ↔ Me a Li b
(6.3)
where Me is a metal such as Al, Sn and Al or a semi-metal such as Si and Ge. Among
them, Si and Sn have a distinguished position due to the technical and/or economic
advantages [17, 18]. Table 6.1 compares the theoretical capacity of selected materials
with that of graphite. Despite the much greater theoretical capacity achievable, the
major challenge associated with the development of metallic/semi-metallic anodes
is the high volume changes involved in the reaction scheme (6.3), as indicated in
Table 6.1.
In the last two decades, there has been a significant deal of research worldwide,
aiming to improve of the cyclability of metallic/semi-metallic anodes, including Sn
and Si. The effect of volume changes on the cycling performance can be reduced
by decreasing the particle sizes of Si [17] and Sn [18]. However, the decreasing
of the particle sizes alone cannot completely eliminate the capacity degradation,
particularly after few tens of cycles. An effective way to mitigate the failure of the
metallic anodes is to incorporate (or encapsulate) Sn or Si into carbon nanostructures
which can effectively buffer the volume changes of the active material and also
promotes the electrical conductivity of the anode.
An attractive feature of molten salt-based methods is their capability for the fabrication of carbon nanocomposites, in which a metallic second phase is encapsulated
by graphitic carbon layers [4, 19–22].
Table 6.1 Lithiation–delithiation characteristics of different anode materials [18]
Metal/semi-metal Li
Si
Al
Ge
Sn
Al
Graphite
Lithiated
compound
Li
Li 22 Si 5 Al 4 Li 9 Li 22 Ge 5 Li 22 Sn 5 AlLi LiC 6
Theoretical
capacity
(mAh g −1 )
3800
4200
2234
1600
994
993
372
Volume change
(%)
Dendritic
growth
323
–
370
300
97
9
6 Applications of Carbon Nanostructures Produced in Molten Salts
particles as well as the electrical disconnection between the particles and the current
collector, and thus poor cyclability [17, 18].
6.2 Metal–Carbon Nanocomposites as Anode Materials
for Li-Ion Batteries
The replacement of graphite by a metallic anode can offer benefits such as a higher
specific capacity, at least during the initial cycles, due to more lithium ions that can
contribute to the reaction scheme (6.3) compared to that of (6.1):
aMe + bLi
+
+ be ↔ Me a Li b
(6.3)
where Me is a metal such as Al, Sn and Al or a semi-metal such as Si and Ge. Among
them, Si and Sn have a distinguished position due to the technical and/or economic
advantages [17, 18]. Table 6.1 compares the theoretical capacity of selected materials
with that of graphite. Despite the much greater theoretical capacity achievable, the
major challenge associated with the development of metallic/semi-metallic anodes
is the high volume changes involved in the reaction scheme (6.3), as indicated in
Table 6.1.
In the last two decades, there has been a significant deal of research worldwide,
aiming to improve of the cyclability of metallic/semi-metallic anodes, including Sn
and Si. The effect of volume changes on the cycling performance can be reduced
by decreasing the particle sizes of Si [17] and Sn [18]. However, the decreasing
of the particle sizes alone cannot completely eliminate the capacity degradation,
particularly after few tens of cycles. An effective way to mitigate the failure of the
metallic anodes is to incorporate (or encapsulate) Sn or Si into carbon nanostructures
which can effectively buffer the volume changes of the active material and also
promotes the electrical conductivity of the anode.
An attractive feature of molten salt-based methods is their capability for the fabrication of carbon nanocomposites, in which a metallic second phase is encapsulated
by graphitic carbon layers [4, 19–22].
Table 6.1 Lithiation–delithiation characteristics of different anode materials [18]
Metal/semi-metal Li
Si
Al
Ge
Sn
Al
Graphite
Lithiated
compound
Li
Li 22 Si 5 Al 4 Li 9 Li 22 Ge 5 Li 22 Sn 5 AlLi LiC 6
Theoretical
capacity
(mAh g −1 )
3800
4200
2234
1600
994
993
372
Volume change
(%)
Dendritic
growth
323
–
370
300
97
9