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6 Applications of Carbon Nanostructures Produced in Molten Salts
Graphite is currently employed as the anode material in commercial Li-ion batteries for various applications. However, the theoretical capacity of graphite, based
on the intercalation of Li into its lattice structure, is limited to a maximum theoretical
value of 372 mAh g
−1 , due to the formation of LiC 6 :
6C + Li
+
+ e ↔ LiC 6
(6.1)
Therefore, graphite has to be replaced by alternative anode materials with higher
capacities, particularly for automotive applications. The new material used as the
anode should be comparable with graphite in terms of the processing costs and should
also be capable of being produced by sustainable methods. A number of materials
with a Li storage capacity higher than graphite have been investigated as possible
anode materials. Among them, SnO 2 is one of the most promising candidates due to
its high theoretical specific capacity of 789 mA h g
−1 and low cost. It, however, suffers
from large volume changes as much as 300% associated with full lithium insertion and
extraction processes leading to the loss of electrical contact and therefore failure of
the electrode. The other limitation of SnO 2 in this application associates with its poor
electronic conductivity which negatively affects the electrochemical performance of
the electrode. An effective strategy to tackle these restrictions is the incorporation of
graphene with SnO 2 nanoparticles [7–11].
Exhibited in Fig. 6.1, a SnO 2 –graphene composite material was prepared by hightemperature oxidation of SnCl 2 [12–15] on graphene nanosheets produced in molten
LiCl, for use as anode material in Li-ion batteries. The green and simple strategy
used to prepare this SnO 2 -loaded graphene nanosheets was based on heating of a
mixture of graphene and SnCl 2 to a temperature of 580 °C. Upon the evaporation of
SnCl 2, the following reaction occurs:
SnCl 2 (g) + O 2 (g) = SnO 2 (s) + Cl 2 (g) )G
◦ = −182 KJ (at 580
◦ C)
(6.2)
Reaction 6.2 leads to the deposition of SnO 2 on the graphene nanosheets, such
as shown in Figs. 6.1a and b. In this composite material, highly crystalline SnO 2
nanocrystals of 5–20 nm in size are anchored on graphene nanosheets with a perfect
connection as can be depicted from Fig. 6.1c. The composite material, fabricated
by combining the molten salt-produced graphene with SnO 2 nanocrystals, exhibited
a reversible capacity of about 1000 mAh g
−1 after 100 cycles at a current density
of 1C in the potential range of 0.003–3 V versus Li
+ /Li. This capacity is about
three times more than the capacity of graphite [3]. It should be mentioned that
the electrochemical performance of SnO 2 nanocrystals is poor, reaching less than
200 mAh g
−1 after 100 cycles [16]. This is mainly due to the poor conductivity and
also the large volume changes of SnO 2 during charge–discharge processes, leading
to the fatigue failure and disintegration of the electrode. The high performance of
the SnO 2 –molten salt graphene composite is attributed to the presence of graphene
nanosheets which provide excellent electronic contacts between individual SnO 2
particles and clusters, overcoming the loss of the mechanical and electronic integrity
of the active material over charge–discharge cycling.
6 Applications of Carbon Nanostructures Produced in Molten Salts
Graphite is currently employed as the anode material in commercial Li-ion batteries for various applications. However, the theoretical capacity of graphite, based
on the intercalation of Li into its lattice structure, is limited to a maximum theoretical
value of 372 mAh g
−1 , due to the formation of LiC 6 :
6C + Li
+
+ e ↔ LiC 6
(6.1)
Therefore, graphite has to be replaced by alternative anode materials with higher
capacities, particularly for automotive applications. The new material used as the
anode should be comparable with graphite in terms of the processing costs and should
also be capable of being produced by sustainable methods. A number of materials
with a Li storage capacity higher than graphite have been investigated as possible
anode materials. Among them, SnO 2 is one of the most promising candidates due to
its high theoretical specific capacity of 789 mA h g
−1 and low cost. It, however, suffers
from large volume changes as much as 300% associated with full lithium insertion and
extraction processes leading to the loss of electrical contact and therefore failure of
the electrode. The other limitation of SnO 2 in this application associates with its poor
electronic conductivity which negatively affects the electrochemical performance of
the electrode. An effective strategy to tackle these restrictions is the incorporation of
graphene with SnO 2 nanoparticles [7–11].
Exhibited in Fig. 6.1, a SnO 2 –graphene composite material was prepared by hightemperature oxidation of SnCl 2 [12–15] on graphene nanosheets produced in molten
LiCl, for use as anode material in Li-ion batteries. The green and simple strategy
used to prepare this SnO 2 -loaded graphene nanosheets was based on heating of a
mixture of graphene and SnCl 2 to a temperature of 580 °C. Upon the evaporation of
SnCl 2, the following reaction occurs:
SnCl 2 (g) + O 2 (g) = SnO 2 (s) + Cl 2 (g) )G
◦ = −182 KJ (at 580
◦ C)
(6.2)
Reaction 6.2 leads to the deposition of SnO 2 on the graphene nanosheets, such
as shown in Figs. 6.1a and b. In this composite material, highly crystalline SnO 2
nanocrystals of 5–20 nm in size are anchored on graphene nanosheets with a perfect
connection as can be depicted from Fig. 6.1c. The composite material, fabricated
by combining the molten salt-produced graphene with SnO 2 nanocrystals, exhibited
a reversible capacity of about 1000 mAh g
−1 after 100 cycles at a current density
of 1C in the potential range of 0.003–3 V versus Li
+ /Li. This capacity is about
three times more than the capacity of graphite [3]. It should be mentioned that
the electrochemical performance of SnO 2 nanocrystals is poor, reaching less than
200 mAh g
−1 after 100 cycles [16]. This is mainly due to the poor conductivity and
also the large volume changes of SnO 2 during charge–discharge processes, leading
to the fatigue failure and disintegration of the electrode. The high performance of
the SnO 2 –molten salt graphene composite is attributed to the presence of graphene
nanosheets which provide excellent electronic contacts between individual SnO 2
particles and clusters, overcoming the loss of the mechanical and electronic integrity
of the active material over charge–discharge cycling.