Page 282 - Polymer-based Nanocomposites for Energy and Environmental Applications

254 Polymer-based Nanocomposites for Energy and Environmental Applications

SEI film on the surface of the anode, which leads to better reversibility and cyclic life
of the anode. One disadvantage with such packing is the reduced packing density of
the electrodes, which leads to low volumetric energy density [153,162]. Spinel mate-
rial such as Li 4 Ti 5 O 12 has been explored as possible replacement for the graphite
anode materials because of their low cost, ease of synthesis, long-term stability,
and better safety features during the charging and discharging process. To improve
the overall performance, especially to increase the intrinsic ionic conductivity
1
(10–13 S cm ), among various methods, the most attractive method is to coat the
material with a nanothickness layer of a conducting polymer. Polyaniline [163],
poly(3,4-ethylenedioxythiophene) (PEDOT) [164], and polythiophene [165] have
been explored as the conducting polymer coating to improve the electrochemical per-
formance of the Li 4 Ti 5 O 12 anode.
Xu et al. coated the Li 4 Ti 5 O 12 with polythiophene via an in situ oxidative polymer-
ization method resulting in a core-shell structure. The polymer nanocomposite
showed specific discharge capacity of 172 mAh g 1 at 0.1 C discharge rate, which
is better than the bare Li 4 Ti 5 O 12 or PANI-coated Li 4 Ti 5 O 12 [163]. The material
showed ultralong stability and cycle life even at very high discharge rate. The dis-
charge capacity of the material was 140.3 mAh g 1 at 10 C after 500 cycles. The
excellent electrochemical performance can be attributed to the increase in the elec-
tronic conductivity by applying a thin layer of conducting polymer that can facilitate
electron transmission during the charge/discharge process. Tin oxide in its various
nanostructures including nanotubes, nanowires, and nanoparticles has been explored
as anode material for the Li-ion batteries [166–168]. Liu et al. synthesized sandwich-
like rGO/SnO 2 /PANI nanocomposite by spreading SnO 2 nanoparticles on the 2D
layers of the graphene oxide sheets and subsequently covering the SnO 2 with a nano-
thickness layer of PANI to increase the electric connectivity in the structure con-
taining SnO 2 and graphene. The resulting structure was found to be flexible to
accommodate for the volume expansion during the insertion/extraction process and
inhibit particle growth during synthesis and during the operation leading to enhanced
cyclic life. The rGO/SnO 2 /PANI composite showed very high energy density
1
397 mAh g 1 at high discharge rate of 10 A g . Fig. 9.3 shows the different aspects
of rGO/SnO 2 /PANI.
Titanium oxide is another oxide material that has shown immense potential to
replace the graphite as anode material due to its high Li insertion/extraction potential,
high reversible capacity, lower volume expansion during the charging/discharging
process, and longer cyclic stability [170]. Not only it shows poorer theoretical capacity
1
(330 mAh g ) in comparison with graphite, but also its inherently low electric con-
ductivity is another barrier to its application as anode. Zheng et al. prepared PANI-
TiO 2 nanocomposite with varying percentage of PANI by mechanical mixing or solid
coating method. It was found that composite with 15% PANI showed highest capacity
1
1
of 281 mAh g 1 at 20 mA g discharge rate. At high discharge rate of 200 mA g ,
after 100 cycles, the nanocomposite with 15% PANI could retain 43.7% of its initial
1
capacity, 168.2 mA g . Coating of PANI helps the particles to remain electronically
connected and offers electrically conductive path for the electron transfer between
active particles, substrate, and the electrolyte [170].