Page 316 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer nanocomposites for lithium battery applications 285

and conductive carbonaceous particles has successfully led to LIBs with high
capacity, high rate capability, and excellent cycling stability [9,10].
In this chapter, the latest development and innovative applications of PNCs
for electrolytes, separators, and electrodes have been reviewed and discussed.

10.2 Composite electrolytes and separators

Present energy storage and production systems are obliged to use organic solvents as
one of the electrolyte component that carries the risks of leakage and fire hazard [11].
Manufacturers are forced to enclose the cell components into heavy packs so that the
increased safety regulations are met. Such heavy protective packing is compensated
against overall amount of ready-to-use active materials, which then dampens the total
energy output of the battery. A paradigm shift from liquid electrolyte-based battery
systems [12] to all-solid batteries will potentially enhance the overall performance
of the energy storage and conversion devices. Improved safety can be achieved
by a complete replacement of organic carbonate-based liquid electrolytes by ion-
conducting polymeric electrolytes for ambient temperature energy storage devices
[13], thus leading to facile and leak-free fabrication, flexible geometry and compact-
ness, reliability, and reduced weight [14].
A polymer composed of macromolecules where substantial portion of the consti-
tutional units contains ionic or ionizable groups or both is termed as polymer electro-
lyte, polyelectrolyte, or polymeric electrolyte [15]. Nevertheless, an ionically
conducting solution of a salt in a polymer matrix can be called as solid polymer elec-
+

trolyte (SPE), for example, a solution of lithium salt (Li X ) in poly(ethylene oxide)
(PEO) matrix, where the ionic conductivity is arising from the mobility of lithium

cations and anions (counter ions, X ) under an electric field. In general, SPEs can
be prepared in two classes, namely, polymer in salt (PiS) system where the concen-
tration of salt is higher than the polymer matrix and salt in polymer (SiP) system where
the concentration of polymer (or repeating units) is higher than the selected salt [13].
The evolution of polymer electrolyte has gone through three stages [16], namely,
(i) solid polymer electrolyte (SPE), (ii) gel polymer electrolyte (GPE), and
(iii) polymer composite electrolyte (PCE). A solid polymer electrolyte is a solid
ion-conducting medium and also serves as a separator, where the polymer host
(solvent) can solubilize a salt without involving any types of organic liquids. The
ion conduction in GPE majorly happens through the plasticizer/solvent/ionic liquid
that is added into the polymer matrix, therefore higher than that of SPEs at room
temperature [17-19]. A polymer composite that functions as a separator and an
ion-conducting medium (electrolyte) can be termed as a PCE. A PCE is a multiphase
and multidomain material; it conducts ions and meanwhile is an electric insulator;
a PCE exists in either all-solid- or gel-like form and should effectively separate the
cathode and anode compartments.

SPEs based on PEO and Li-X (X¼ClO 4 ,BF 4 , AsF 6 ,PF 6 ,CF 3 SO 3 , (CF 3 SO 2 ) 2 N ,

etc.) have been in the spotlight since Wright et al. reported in 1973, which a mixture of
PEO and alkaline salts exhibited ionic conductivity [20]. PEO is a highly crystalline