Plasticized and gel polymer electrolytes

In 2001, a dye-sensitized solar cell assembled with a gel network polymer electrolyte based on polysiloxane and PEO, containing 20 wt% of Lil, 5 wt% of h and 150 wt% of the mixture ethylene carbonate (EC)/propylene carbonate (PC) (3 1 v/v) was reported. EC is a high viscosity solvent with high dielectric constant, which is favorable for salt dissociation. However, this material has a tendency to crystallize at low temperature, causing phase separation between the plasticizer and the polymer matrix. Thus, organic solvents such as PC are used to form binary organic solvents with EC and homogeneous gel polymer electrolytes can be obtained. The fully cross-linked electrolyte presented ambient conductivity of 1.1 x 10 S cm and 

Interesting results have also been obtained using y-butyrolactone (GBL) as plasticizer for P(EO-EPI) copolymer. For the electrolyte prepared with GBL, P(EO-EPI)87-13,15 wt% of Nal and h for example, the maximum ionic conductivity changed from 3 x 10 S cm to 1 x 10 S cm after addition of 50 wt% of GBL. The apparent diffusion coefficient of ionic species in the electrolyte with and without plasticizer was estimated using complex electrochemical impedance spectroscopy (EIS) and the equivalent circuit (Rg. 10.6) was used to fit the data according to the 

6 Nyquist diagrams of the impedance spectra obtained for poiymer eiectroiyte fiims sandwiched between pianar Pt eiectrodes. Experimentai data are represented by symbois and soiid iines correspond to the fitting using the equivaient circuit shown in the inset. The poiymer eiectroiytes are based on P(EO-EPi), Nai/i2 (O) with piasticizer (50 wt% GBL) and ( ) without piasticizer. 

GBL has been used as plasticizer for electrolytes for application in batteries, and it is well known to be able to coordinate LL ions, contributing to the dissolution of lithium salts in polymer systems. Therefore, GBL also made possible the substitution of Nal for Lil in the polymer electrolye, as shown in the plots of ionic conductivity in Fig. 10.7. As opposed to what 

8 Ionic conductivity as a function of Lil concentration for the polymer electrolyte P(EO-EM)/GBL/Lil/l2, upon addition of ( ) 30% or (A) 70% of GBE. The figure also shows a picture of liquid electrolyte (left) and a gel polymer electrolyte containing 70 wt% GBL (right). As can be seen, almost no fluidity is observed at room temperature, even after addition of 70 wt% of GBL. This is an important feature for application as electrolyte in a solar cell. 

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