**2.5 Mixed solvent system**

On the other hand, the increase of conductivity in binary solvent system is proven by Deepa et al. (2002). In this study, poly(methyl methacrylate) (PMMA)–based polymer electrolytes containing lithium perchlorate (LiClO4), with a mixture of solvents of propylene carbonate (PC) and ethylene carbonate (EC) were prepared. The maximum ionic conductivity of 10-3 S cm-1 was obtained and it was increased by two orders of magnitude as compared to polymer electrolyte system with single solvent. Synergistic effect is the major factor to increase the ionic conductivity in this mixed solvent system. Different physicochemical properties of the individual solvents come into play and contribute to high ionic conductivity in the presence of the effect. The preparation on EC/PC/2–methyl–tetrahydrofuran (2MeTHF) ternary mixed solvent electrolyte had been done by Tobishima and co–workers. They found out that the discharge capacity of Li/amorphous V2O5–P2O5 cells with a ternary mixed solvent electrolyte are slightly better than for cells with EC/PC binary mixed solvent electrolytes.

#### **2.6 Addition of inorganic fillers**

Utilization of common additives such as inorganic fillers and plasticizers is the effective and efficient approach to enhance the ionic conductivity. Fillers (also known as reinforcing fillers) are divided into two types: inorganic and organic. Variety types of inorganic fillers have been used, including mica, clay, titania (TiO2), fumed silica (SiO2) and alumina (Al2O3). On the other hand, graphite fibre and aromatic polyamide are some examples of organic fillers. The main objectives of dispersion of inorganic filler are to alter the properties of the polymer, enhance processability and improve the mechanical stability in the polymer electrolyte system. Dispersion of inorganic fillers can also improve the ionic conductivity in the polymer electrolyte. Besides improving the lithium transport properties, the inclusion of ceramic filler has been found to enhance the interfacial stability of polymer electrolytes (Osinska et al., 2009).
