**2. Methods to improve ionic conductivity**

Ionic conductivity is the main aspect to be concerned in the solid polymer electrolytes. Ionic conductivity is defined as ionic transportation from one site to another through defects in the crystal lattice of a solid under the influence of an external electric field. Much effort has been devoted for developing highly conducting polymer electrolytes. Several ways have been done to modulate the ionic conductivity of polymer electrolytes, for instance, random and comb–like copolymer of two polymers, polymer blending, mixed salt and mixed solvent systems as well as impregnation of additives such as ceramic inorganic fillers and plasticizers.
