Page 274 - Polymer-based Nanocomposites for Energy and Environmental Applications

246 Polymer-based Nanocomposites for Energy and Environmental Applications

conductivity below 60°C. Polymer nanocomposite with a polymer matrix and an inor-
ganic nanomaterial as filler is an attractive way to increase the low-temperature ionic
conductivity and the mechanical strength of the polymer electrolytes. The fillers pro-
mote the mechanical strength by the network of polymers in the bulk matrix, whereas
ionic conductivity is raised by the presence of high surface area of the dispersed filler.
Weston and Steele first used α-alumina as filler for the PEO polymer matrix. It was
found that 10% vol. of the alumina did not bring any change in the ionic conductivity
but greatly improved the high-temperature mechanical stability of the polymer
[74,75]. Generally, two different types of fillers have been explored in the literature:
+
(1) fillers that directly allow the Li ions and (2) fillers that indirectly assist in improv-
ing the ion conductivity. Various inert inorganic fillers such as TiO 2 [76,77], SiO 2
[78,79],Al 2 O 3 [76], ZrO 2 , mesoporous material, MMT, and others are used.
Klongkan et al. prepared polymer nanocomposite with PEO as polymer matrix and
various amounts of plasticizer LiCF 3 SO 3 and nanosized alumina as filler. It was found
that the addition of plasticizer and nanoalumina increases the ionic conductivity from
5
10 7 to 10 . Differential scanning calorimetry and X-ray diffraction (XRD) studies
indicated that the conductivity increase was due to the decrease of crystallinity upon
the addition of lithium salt, nanoalumina, and plasticizers into the SPE system. The
mechanical properties of PEO tended to decrease with the addition of lithium salts,
nanoalumina, and plasticizers [80]. In addition to PEO, poly(methyl methacrylate)
(PMMA) is also considered as attractive polymeric matrix [81,82]. Kaskhedikar
[83] studied a polymer nanocomposite made from poly[(bis(2-methoxyethyl)
amino)1 x(n-propylamino)x-phosphazene] (BMEAP) with dissolved LiCF 3 SO 3
and dispersed Al 2 O 3 nanoparticles (40 nm). Membranes with good mechanical stabil-
ity were obtained. Low ionic conductivities were found in particle-free membranes
with maximum conductivities at 10 wt% LiCF 3 SO 3 ranging from 3.1 10 7 Scm 1
at 30°C to 1.8 10 5 Scm 1 at 90°C. For the composite membranes, addition of
2 wt% Al 2 O 3 nanoparticles leads to a steep increase of the conductivity by almost
two orders of magnitude as compared with the homogeneous membranes. The highest
room temperature conductivity for the investigated BMEAP-LiCF 3 SO 3 -Al 2 O 3
1
composite systems was 10 5 Scm .
A polymer electrolyte based on PEO hyperbranched polymer poly[bis(triethylene
glycol)benzoate] capped with an acetyl group (HBP) and BaTiO 3 , a nanofiller, was
used. The conductivity of the composite polymer electrolyte PEO-10 wt% HBP with
Li(CF 3 SO 2 ) 2 N-10 wt% LiPF 6 as a lithium salt and 10 wt% BaTiO 3 was found to be
1.6 10 4 Scm 1 at 25°C and 1.5 10 3 Scm 1 at 60°C in a O/Li ratio of 10. The
lithium rechargeable batteries consisted of this highly conductive composite polymer
electrolyte and the 4 V class cathode, LiNi 0.8 Co 0.2 O 2 , showed excellent charge-
discharge cycling performance. The initial cathode discharge capacity of
154 mAh g 1 declined only 0.1%/cycle during the first 30 cycles at 60°C [84]. Shim
et al. prepared a series of polymer nanocomposite electrolytes by the organic and inor-
ganic copolymer PEGMA and MA-POSS as polymer matrix and polyethylene glycol-
grafted graphene (PGO) as nanofiller material. The ionic conductivity of a polymer
nanocomposite with 0.2 wt% of PGO showed 2.1 10 4 Scm 1 at 30°C compared
with the 1.1 10 5 for BCP at 30°C. The thermal and mechanical stability of the