Page 277 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer nanocomposite materials in energy storage: Properties and applications 249

conductivity, poor cyclic stability, and slow electrochemical reaction kinetics and
hence poor power density [126].V 2 O 5 in various nanostructure forms such as nano-
rolls [127], nanorods [128], nanotubes [129], nanocable array [130], and nanobelts
[114] has been synthesized and tested as a cathode material [131]. One way to increase
its performance by increasing the electronic conductivity is to make polymer
nanocomposites with conducting polymers. The conducting polymer nanocomposites
consist of layers of conductive polymers sandwiched between the layers of V 2 O 5 .
Both the oxide and the conducting polymers are electrochemically active, which is
very attractive. Ferreira et al. synthesized a supermolecular structurer of PANI and
V 2 O 5 using electrostatic layer-by-layer technique. Strong ionic interaction and hydro-
gen bonding between the components led to improved intercalation capacity [132].
Ponzio et al. prepared nanocomposite of polyaniline and V 2 O 5 using reverse micelle
method to study their structure and electrochemical performance. It was found that
although V 2 O 5 nanofibers show large capacity fade, a polymer nanocomposite con-
1
taining 30% polyaniline exhibits stable capacity of 300 mAh g . It was also
observed that the polymer composite is able to retain the structure in far more effec-
tively than V 2 O 5 on electrochemical cycling. The nanocomposite showed improved
performance because polyaniline was able to buffer the stress generated due to volume
changes during cycling leading to improved capacity [133]. Zhao et al. prepared poly-
mer nanocomposite of V 2 O 5 /PPy using in situ polymerization of pyrrole monomer on
the surface of the nanosized V 2 O 5 prepared by hydrothermal means. The electrochem-
ical results showed that the initial and after 200 charging/discharging discharge capac-
ity of the composite in the voltage range 2–4 V was 208 and 170, respectively,
whereas the discharge capacity of V 2 O 5 without PPy descended to 130 mAh g 1 after
100-cycle charge/discharge process. The improved performance of V 2 O 5 /PPy is
ascribed to the excellent electric contact between PPy and V 2 O 5 in the polymer com-
+
posite and faster kinetics of the Li intercalation/deintercalation process. The PPy
layer on the surface of V 2 O 5 plays a role of plastic protecting shell, and the collapse
of V 2 O 5 due to volume expansion during the charge/discharge process can be
prevented effectively [134].
Recently, Chao et al. synthesized V 2 O 5 nanoarray-based positive electrodes pre-
pared by growing a V 2 O 5 nanobelt array (NBA) directly on a three-dimensional
(3D) graphene foam (ultragraphite foam), followed by coating the V 2 O 5 with a meso-
porous thin layer of the conducting polymer poly(3,4-ethylenedioxythiophene)
(PEDOT). The UGF-V 2 O 5 /PEDOT core-shell polymer nanocomposite cathode
showed ultrastable high capacity of 297 mAh g 1 at 1°C [135]. Recently, Yan
et al. [104] synthesized polyaniline-coated LiVPO 4 F via sol-gel synthesis method
followed by a self-assembly method. The XRD results suggest that very high-purity
LiVPO 4 F/PANI composite with tavorite LiFePO 4 (OH) structure was formed with no
other secondary phase being added to LiVPO 4 F. TEM results show that the particle
size in the bare LiVPO 4 F and polyaniline-coated LiVPO 4 F was between 100 and
200 nm. The electrochemical results are also shown in Fig. 9.2.In Fig. 9.2B, from
the initial charge/discharge behavior of the pure and PANI-coated LiVPO 4 F cathodes
at a rate of 0.1 C, the PANI-coated LiVPO 4 F electrode shows an initial discharge
+
capacity of 149.3 mAh g 1 in the potential range of 3.0–4.5 V vs Li /Li, which is