Page 320 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer nanocomposites for lithium battery applications 289

of LLTO was due to the variations in grain size and possible grain boundary
composition. Doping with other metal cations also influences the bulk conductivity
of LLTO. They can also form a garnet-related structure (Li 5 La 3 Ta 2 O 12 ) exhibiting
good lithium-ion conductivity.
Phosphates exhibit good lithium-ion conduction, such as Li 1+x Al x Ge 2 x (PO 4 ) 3
(LAGP), Li 1+ x Ti 2 x Al x (PO 4 ) 3 (LTAP), and LiTi 0.5 Zr 1.5 (PO 4 ) 3 . Among these, the
zirconium-based phosphate has the lowest ionic conductivity [39]. A polyacryloni-
trile-LiClO 4 complex containing 15 wt% Li 0.33 La 0.55 TiO 3 (LLTO) nanowires
exhibited an ionic conductivity of 2.4 10 4 Scm 1 at room temperature [40].

10.2.1.2 Naturally-sourced materials
Cellulose is a nature-abundant polysaccharide, made of repeat units of monomer
glucose. It can be modified to form carboxy methyl cellulose (CMC), cellulose nitrate,
cellulose acetate, or cellulose sulfate, and most of them are used in PCEs as rein-
forcing agents. The related nanosized fillers are in the form of cellulose microfibrils
[41,42] cellulose sheets [43], or cellulose whiskers [44]. Other materials such as
carrageenan [45] and xanthan gum [46] have also been used in PCEs. In general, these
materials improved mechanical properties, interfacial resistance, and ionic mobility.
Other than the plant-derived cellulose-based systems, animal-derived materials
such as chitin have been applied in PCEs. Chitin is the second most important natural
polymer in the world and is extracted from two marine crustaceans, that is, shrimp and
crabs [47]. Chitin (depending on the origin of the polymer) with a 50% of degree
of deacetylation becomes soluble in aqueous acidic media and is named as chitosan.
Both chitin and chitosan have been used to reinforce PCEs [48,49].

10.2.1.3 Porous materials
Ordered mesoporous materials such as zeolite family of materials (MCM-41 and
SBA-15) are unique materials for catalysis, separation, or electronics applications
due to their well-ordered microstructure, high surface area, and specific pore size
[50]. SBA-15 exhibits uniform, long, and connecting tubular channels of variable pore
sizes between 5 and 30 nm along with large surface area [51]. SBA-15 has been found
to enhance the interphase stability, ionic conductivity, and even electrochemical sta-
bility window [50,52], when applied in PCEs. Metal-organic frameworks (MOFs) are
microporous solids consisting of an infinite network of metal centers (or inorganic
clusters) bridged by simple organic linkers through metal-ligand coordination bonds
[53]. They are widely used in sensors, ion exchange, catalysis, gas storage, purifica-
tion, separation, and sequestration. Recently, Wiers and coworkers demonstrated an
increase in ionic conductivity of a solid electrolyte by the addition of lithium
isopropoxide to a Mg-based MOF [54], followed by soaking in a conventional liquid
electrolyte. Yuan et al. [55] proposed a Zn-based MOF-5 as a novel filler for PEO-
based nanocomposite electrolytes, showing improved electrochemical properties in
LIBs. Besides, a detailed study by Gerbaldi et al. [56] demonstrated that a PEO-based
PCEs encompassing an ad hoc synthesized aluminum benzenetricarboxylate