**4.2 Tensile test: 70PAN-30NaF-(1–4 wt%) Al2O3 composite**

To effect the practical use of a polymer electrolyte, the electrolyte must remain structurally stable during manufacturing, cell assembly, storage, and usage, prevent flow from occurring within the cell to prevent self-discharge, and be easy to prepare in a repeatable manner. That is, mechanical strength is also an important factor when manufacturing polymer electrolytes. As noted earlier, incorporating additives such as ceramic powder can strengthen the dimensional stability of electrolyte membranes [17–20].

The addition of nanoparticles increased both the modulus and the strength of the polymer nanocomposites. Additionally, the toughness (area under the stress–strain curve before rupture) increased significantly. **Figure 7** shows the tensile strength (the maximum stress in the stress–strain curve, MPa) and Young's modulus (the slope of the stress–strain curve in the low strain region) as a function of nanoparticle volume content. Both the tensile strength and Young's modulus increased with increasing functionalized particle loading. Compared to the pure polymer, the strength and Young's modulus of the 4 wt% filled nanocomposite sample increased by approximately 99%. The imagination of the nanoparticles was observed to have a greater effect on the Young's modulus. Moreover, the relatively uniform distribution of Al2O3 particles and decrease in interparticle distance with increasing particle loading in the matrix results in polymer nanocomposites having increased resistance to indentation. For a given volume fraction, nanoparticles are much closer to each other than microparticles in the matrix, and hence nanoparticles will more strongly resist the penetration of the indentation in the matrix [21]. This results in higher microhardness for nanocomposites than that of polymers at a constant volume fraction of particles.

#### **4.3 DC conductivity studies**

#### *4.3.1 Conductance spectra for PAN:NaF gel polymer electrolytes*

**Figure 8** shows the ionic conductivity in addition to NaF salt with the host polymer PAN. The conductivity increased with the enhancement of NaF salt from 10 to

**Figure 7.** *Tensile test of 70PAN-30NaF-(1–4 wt%)Al2O3Composite.*

*Structural, Optical, and Electrical Studies of PAN-Based Gel Polymer Electrolytes… DOI: http://dx.doi.org/10.5772/intechopen.98825*

**Figure 8.** *Composition dependence of conductivity in the PAN+NaF system.*

30 wt%. For 40 wt% NaF salt, the ionic conductivity was decreased. **Table 4** gives the ionic conductivity values. With the doping of NaF salt, the number of free ions also increased in the host polymer, resulting in enhanced conductivity. At higher concentrations, the enhanced viscosity of the polymer reduced the ionic conductivity. For 30 wt%, NaF shows a higher conductivity of 1.82 x 10−4 S cm−1 due to its less crystalline nature compared to other compositions [16–18].

Conductivity studies were carried out for all the prepared polymer electrolytes to understand the conduction mechanism. **Figure 9** shows the ionic conductivity versus nanofiller (Al2O3) concentration of the polymer electrolyte PAN+NaF complexed system with varying weight percentages of nanofiller in the temperature range 303 K to 373 K. **Table 4** presents the conductivity data at room temperature and at 373 K. We conclude that the conductivity increases as the nanofiller content increases up to 4 wt% due to the high.

Amorphous nature of the polymer electrolyte, which provides more free mobile protons (carriers), thus giving rise to higher conductivity [22].

The enhancement in conductivity is not only due to the increment of mobile charge carriers but also due to ethylene carbonate (EC), which allows greater dissolution of the electrolyte salt and nanofiller, resulting in an increased number of charge carriers and hence an increase in conductivity. The maximum value of conductivity obtained at room temperature is 4.82 × 10–3 S cm−1. This conductivity value is 10 orders greater than that of pure PAN (10−14 S cm−1), as reported by Pan and Zou [23]. The conductivity increases with the incorporation of nanofiller wt %, which might be due to ion pair or aggregate formation [24]. The polymer electrolytes lead to an increase in the viscosity of the polymer electrolyte film due to the incorporation of a large amount of salt and nanofiller content, which reduces

**Figure 9.** *Ion conductivity (*σ*) of polymer electrolyte films as a function of wt% of Al2O3 concentration.*


**Table 4.**

*DC conductivity, Ea, ionic transference numbers of various compositions of PAN:NaF gel polymer electrolytes.*

proton transportation and impedes the mobility of charge carriers, resulting in a decrease in proton conductivity.

**Figure 10** Illustrates the variation of ionic conductivity with temperature for different wt% of Al2O3. The ionic conductivity was calculated using the formula given in Eq. 3.

$$
\boldsymbol{\sigma} = \mathbf{t} / \mathbf{AR}\_{\boldsymbol{b}} \tag{3}
$$

where t and A represent the thickness and the area of the electrolyte specimen, respectively [25]. Rb is the bulk resistance of the electrolyte obtained from the complex impedance measurement. The ionic conductivity depends on the overall mobility of ion species present in the electrolyte and the polymer, which is determined by the free volume made by filler and plasticizer around the polymer chain. In the present study, conductivity enhancement was observed when the Al2O3 filler and EC plasticizer were incorporated into the polymer salt system. The polymer electrolytes considered in the present study exhibited an Arrhenius type of conduction [26]. The polymer electrolyte containing 3 wt% nanofiller showed an ionic conductivity of 5.96 × 10−3 Scm−1.

#### *4.3.2 Transference number measurements*

To measure the conductivity of prepared polymer electrolytes, the transfer numbers play a vital role. To determine transfer numbers, Wagner's polarization

**Figure 10.** *Log* σ *versus 1000/T of PAN+NaF complexed films for different wt% of Al2O3.*

*Structural, Optical, and Electrical Studies of PAN-Based Gel Polymer Electrolytes… DOI: http://dx.doi.org/10.5772/intechopen.98825*

**Figure 11.** *Polarization current vs. time plot for the PAN:NaF polymer composite at 303 K.*

method can be used. The prepared PAN:NaF sample was placed between two silver electrodes. After the circuit was closed, DC voltage was applied to the sample to measure the polarization current. **Figure 11** shows the final stabilized current values. The polarization current was decreased with respect to increasing time due to predominantly ions [19]. **Table 4** shows the transfer numbers for 10 to 40 wt% NaF doped with PAN as 0.965, 0.972, 0.989, and 0.969.
