Page 582 - Polymer-based Nanocomposites for Energy and Environmental Applications

Hybrid materials based on polymer nanocomposites for environmental applications 535

behavior, which facilitates the charge transport along their backbone. Other advan-
tages of conjugated polymers such as low cost, flexibility, large surface, and ease
to be used for composites make them attractive for battery applications. However,
polymer structure suffers from instability under high-charging/discharging condi-
tions, which can lead to their premature degradation. Furthermore, the voltage of
the battery may fluctuate after successive operation cycles because of the structural
instability of the polymer.
The use of polymer-based composites to enhance the battery performance has been
successfully obtained with several conjugated polymers. The composite can be pre-
pared by combination of conjugated polymers with previously mentioned inorganic
cathode materials. For instance, composites made of V 2 O 5 and PANI were used as
cathode material in LIBs [118] with a large specific capacity ( 270 mAh/g) and high
cyclability ( 3.4%). The high performance of the battery was attributed to an
improved conductivity of the cathode due to PANI and also to its prevention of the
structural change at the interface of the oxide. Other oxide/polymer composites have
been successfully used as cathode materials in batteries with improved characteristics
and stability [119–121]. Another method to prepare composite cathode materials con-
sists of mixing conjugated polymers with nanostructured carbon such as carbon black,
CNTs, or graphene. Indeed, it is known that nanostructured materials offer a large vol-
ume (surface) for intercalation of ions and thus may increase the contact surface with
the electrolyte and reduce the volume changes due to interaction. Besides, the conduc-
tivity of these materials is usually high and consequently can favor the charge trans-
+
port. Finally, a nanosized cathode would reduce the diffusion length for Li ions
transportation, producing a fast with a high rate of charge exchange. For instance,
MWCNT/PANI has been used for cathode material [122] in LIBs with enhanced elec-
tric properties and stability. Incorporation of MWCNTs to the conjugated polymer
reduces the inner resistance and facilitates also thermal dissipation of the cell
and increases thus its specific capacity. SWCNTs with PVK [123] are also used for
cathodes, but compared with MWCNTs, the battery performance is lower.
Graphene/polymer composites have been also investigated for cathode materials.
These composites have some advantages over other carbon-based one, which include
a large contact surface with the host polymer and a very high-electric conductivity,
which provide a fast charge and discharge cathode material. For instance, polyimide
and poly(anthraquinonyl sulfide) have been synthesized in the presence of graphene to
form composites [124] and then used as cathode in LIBs. Very fast charging rate has
been obtained and explained by the fast redox kinetics associated with the fast electron
transfer and the large contact between graphene and the polymer. Covalent func-
tionalization of polymers with graphene has also been investigated [125] to avoid
restacking of graphene sheets in the composites leading to an increased transport
of electrons and ions and consequently an improvement of specific capacity and
the cycle performance.
– Anode materials (negative electrode)
Materials used as an anode in LIBs should address several requirements: (i) high elec-
tronic and ionic conductivities to provide a high-power density, (ii) low chemical