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Polymer nanocomposites for lithium battery applications 287

In many cases, the fillers can be incorporated into the polymer matrix or formed in situ
by various processing techniques.

10.2.1 Fillers
10.2.1.1 Ceramics

According to IUPAC recommendation [24], ceramics are rigid materials that consist
of an infinite three-dimensional network of sintered crystalline grains comprising
metals bonded to carbon, nitrogen, or oxygen. The term ceramic generally applies
to any class of inorganic, nonmetallic product subjected to high temperature during
manufacture or use.
Metal oxides such as SiO 2 [25],Al 2 O 3 [22,26], TiO 2 [23], ZnO [27], and ZrO 2 [28]
have been often used in PCEs. The presence of inorganic fillers improves the ion con-
ductivity of PCEs by two means: [1] increases the overall amorphous phase of the
+
polymer matrix and [2] introduces new Li ion-conducting pathways through the filler
surface regions [26,29,30]. Dissanayake et al. [31] proposed a model based on Lewis
acid-base theory in which the ion conductivity enhancement was due to the interac-
tions between the ionic species and the surface groups of the fillers. An acidic surface
group was found to exhibit the highest conductivity among the fillers studied with
acidic, basic, neutral, and weakly acidic Al 2 O 3 nanoparticles. A schematic represen-
tation of interaction between various nanoparticles with PEO chains and LiSO 3 CF 3
ions is shown in Fig. 10.3.
The mechanical, electrochemical, and interfacial properties of the PCEs are also
generally improved by the addition of inorganic fillers. For example, TiO 2 nano-
particles were generated in situ from a sol-gel reaction between glacial acetic acid
and tetrabutyl titanate; then, the mixture was added in a polymer solution at room
temperature to form PCEs [32]. The hydrolysis and condensation reactions [33] are
as follows:

ð
ð
Ti OC 2 H 5 Þ +4H 2 O ! Ti OHð Þ +4C 2 H 5 OH hydrolysisÞ (i)
4 4
nTi OHÞ ! TiO 2 +2nH 2 O condensationð Þ (ii)
ð
4
Such prepared PCE showed improved electrochemical stability, high tensile strength,
and high ionic conductivity up to 10 4 Ω 1 cm 1 at room temperature [34].
Mixed metal oxides are often used in order to achieve desired electrochemical prop-
erties of PCEs. Ferroelectric materials (BaTiO 3 , PbTiO 3 , and LiNbO 3 ) [35], MgAl 2 O 4
[36], and MgAl 2 SiO 6 [37] can be used as additional fillers in order to improve the
conductivity and interfacial properties of PCEs. The simplified fabrication process
containing metal oxides is sketched in Fig. 10.4.
Glass: Ion conduction in ceramic materials happens through the movement of ionic
defects; such movement requires enormous amount of energy, and these materials
are especially suitable for high-temperature applications. The crystalline, amorphous,
or partially crystalline materials are termed as ceramic, glass, or glass-ceramic,