**1. Introduction**

For the last three decades, ionic solid conducting polymer electrolytes have been used as active potential components in novel battery technology such as electrodes and electrolytes. They have excellent properties including light weight, appreciable mechanical strength, excellent plasticity, flexible processing, and easy fabrication in solid-state battery technology. The main advantages of solid polymer electrolytes are their chemical and physical stability, comparable performance to that of thin films (approx. 1 micrometer), and majority conduction of ions rather than electrons. However, the main drawback of solid electrolytes is interface stress due to electrode charging and discharging. Polymer electrolytes are used for batteries due to their ease of forming thin films with a large internal area; reduced resistance, which increases current density; stable and compatible contact with electrodes; and stability under ambient conditions such as temperature, pressure, and atmosphere to facilitate production on a mass scale.

Among polymer electrolytes, gel polymer electrolytes (GPEs) are a very important class of materials and have been used in electrochemical batteries such as fuel cells and electronic display devices [1–4]. Compared to liquid and solid polymer electrolytes, GPEs are found to be very advantageous. In general, in these types of GPEs, salt provides ions for conduction and solvents provide a medium for this conduction. Plasticizers also help to decrease the glass transition temperature. Sodium may be considered an alternative to lithium as a negative electrode due to its low cost and natural abundance. The softness of this metal enables better electrical property contact with other components in the battery. The addition of nanofillers such as aluminum oxide (Al2O3) to this type of salt-based film rapidly enhances the electrical properties. The present work reports on a polymer electrolyte (PAN+NaF + Al2O3) and is concerned with solid-state electrochemical cells that are based on (PAN+NaF) electrolyte films. Several experimental techniques, such as structural, optical, electrical, tensile strength, differential scanning calorimetry (DSC), and DC conductivity measurements, were performed to characterize these polymer electrolytes. Based on these electrolytes, electrochemical cells were fabricated with anode/polymer electrolyte/cathode configurations. The discharge characteristics of the cell were studied for a load of 100 kΩ.

### **2. Experimental**

#### **2.1 Preparation of plasticized nanocomposite polymer electrolytes**

**Figure 1** illustrates the preparation method of solid polymer electrolytes. **Table 1** shows various compositions of filler incorporated GPEs. Polyacrylonitrile (PAN) with a molecular weight of 1,50,000 g/mol was used as the host polymer and sodium fluoride (NaF) was used as the dopant salt. Ethylene carbonate (EC) was used as a plasticizer in the electrolyte and aluminum oxide (Al2O3) was used as a nanofiller. Solid polymer electrolytes were prepared by mixing PAN and NaF salt in dimethyl formamide (DMF). The solution thus obtained was.

stirred in a magnetic stirrer for approximately 4 hours until we obtained a homogeneous translucent gel after the ethylene carbonate (EC) plasticizer was added to this solution and stirred for approximately 2 hours. After that, the Al2O3 nanofiller was added to this solution and stirred for 48 hours to disperse the nanofiller homogenously in the polymer matrix [2]. The resulting homogeneous mixture was then cast onto polypropylene dishes and the solvent was allowed to evaporate at room

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


#### **Figure 1.**

*Preparation method of solid polymer electrolyte films.*


#### **Table 1.**

*Various compositions of filler incorporated gel polymer electrolytes [5].*

temperature. After the solvent had completely evaporated, the films were peeled off from the polypropylene dishes and pressed under a membrane hot press at a temperature of 40°C. The pressure applied by this method was 3.5 torr/cm2 , and we obtained flexible and self-standing polymer electrolytes. The samples consisted of 1 wt% Al2O3 (A1), 2 wt% Al2O3 (A2), 3 wt % Al2O3 (A3), and 4 wt% Al2O3 (A4). The prepared electrolyte membrane systems had a thickness of approximately 128 μm.

#### **Figure 2.**

*Flow chart techniques for the characterization of solid polymer electrolytes.*

**Figure 3.** *Gel polymer electrolyte film based on nanofillers (Al2O3).*

## **2.2 Materials characterization**

**Figure 2** shows a flowchart for the characterization of solid polymer electrolytes. In the present work, the prepared films were characterized by energy dispersive x-ray spectrometry (EDS) to determine the chemical composition in wt%. The UV–Vis spectrum was recorded by a Hewlett-Packard HP8452A diode array spectrometer. The mechanical properties of the prepared polymer electrolytes were determined using a Universal Tensile Machine (Instron Model 5565, Canada) with a constant crosshead speed of 10 mm/min. The sample dimensions were 25 mm × 40 mm × 0.1 mm. Additionally, DSC thermograms were recorded to measure the glass transition temperature and melting temperature of PAN-based electrolytes by using a Mettler instrument. The samples were heated sequentially from 50–360°C. Finally, transport characteristics and discharge characteristics, such as transference number, open circuit voltage (OCV), short circuit current (SCC), and power density, were determined. at a constant load of 100KΩ. **Figure 3** illustrates a GPE film based on a Al2O3 nanofiller.
