PMMA-Based Polymer Electrolyte Salted With Lithium Triflate, LiCF3SO3 Ionic Conductivity

Figure 2. a a) Conductivity vs wt% EC b) Conductivity vs wt% LiCF3SO3 c) Conductivity vs wt% Al2O3 d) Conductivity vs wt% SiO2 

From the Rb identified by Cole-Cole plot, the ionic conductivity is then be determined from equation (1).Fig. 2 a) gives an rough idea on the crystallinity behaviour of PMMA, addition of EC plasticizer helps to increase the free volume and soften the polymer matrix of the polymer electrolyte thus rotation of polymer chain can occur more readily and the ion transport in the polymer electrolyte is faster as described by Rajendran et al. [12]. The PMMA itself may contains very small amount of minority carrier where addition of EC helps to lower the energy band of the ionic carrier. The maximum conductivity is achieved by addition of 25 wt% plasticizer (EC) which is 6.25 × 10−10 S cm−1. Relatively, the ionic conductivity for this system is low because no lithium salt is being doped into the system as a majority carrier.With the addition of lithium salt (LiCF3SO3) as shown in Fig. 2 b), the ionic conductivity of the polymer film is increased dramatically. The maximum conductivity is achieved at the addition of 25 wt% of LiCF3SO3 gave the conductivity value of 1.36 × 10−5 S cm−1 . Further increase of LiCF3SO3 causes the conductivity to decrease due to the higher salt concentration, the conductivity decrease may be due to the increasing influence of the ion pairs, ion triplets, and higher ion aggregations, which reduces the overall mobility and degree of freedom. In net, the number of effective charge carriers that transit between anode and cathode are relatively reduced, MacCallum et al. [13].In the Fig. 2 c), with additional of 5 wt%, of Al2O3 filler the best ionic conductivity is achieved at 2.05 × 10−4 S cm−1. Referring to the study of Croce et al. [14], Lewis acid-base type oxygen and OH surface groups on alumina grains interact with the cations and anions and therefore providing additional sites creating favourable high conducting pathway in the vicinity of grains for the migration of ions. Dissanayake et al. [14] reported that further addition of the filler grain after its saturated state, the conductivity decreased by blocking effect imposed by the more abundant alumina grains, the long polymer chains is “immobilized” and causes the conductivity to decrease. Same results is observed for Fig. 2 d), with additional of 10 wt% of SiO2 the ionic conductivity increased to 2.15 × 10−5 S cm−1 result by Lewis acid-base reaction between the SiO2 filler surface group with the polymer chain attributed to the enhancement of the ionic conductivity. Scrosati et al. [15] claims that the increment of the ionic conductivity with the addition of SiO2 is due to an increase in free ion concentration. Hyung-Sun Kim et al. [19] reported that SiO2 reduces the glass transition temperature and crystallinity of the polymer, and allows the amorphous polymer to provide specific liquid-like characteristics. In addition, the addition of filler to a polymer matrix is found to improve the ionic conductivity by reducing the crystallization tendency. Further addition of SiO2 causing the ionic conductivity to decrease due to the blocking effect similarly to the effect in Al2O3 where the grains are get close to one another, leading to the decreasing of the conductivity.