Nanofiber Reinforced Composite Polymer Electrolyte Membranes

Abstract

The path breaking studies of Wright and Armand on ionically conducting polymers, called “polymer electrolytes” in the 1970s have opened an innovative area of materials research with potential applications in the power sources industry (Fenton et al., 1973). The main applications of the polymer electrolytes are in rechargeable lithium batteries as an alternative to liquid electrolytes (Chen et al., 2002; Lobitz et al., 1992). The advantages such as no leakage of electrolyte, higher energy density, flexible geometry and improved safety hazards have drawn the attention of many researchers on the development of lithium polymer batteries and other electrochemical devices such as supercapacitors, electrochromic windows, and sensors (Gray, 1991). In batteries being a separator membrane polymer electrolyte must meet the following requirements. 1. high ionic conductivity 2. high cationic transference number 3. good dimensional stability 4. high electrochemical stability and chemical compatibility with both Li anode and cathode material and 5. good mechanical stability. The need for high ionic conductivity arises from the fact that at what rate or how fast energy from a Li-battery can be drained, which largely depends on the extent of ionic mobility in the electrolyte and hence on ionic conductivity. For battery applications, along with high ionic conductivity the electrolyte material must be dimensionally stable since the polymer electrolyte will also function as separator in the battery, which will provide electrical insulation between the cathode and the anode. This implies that it must be possible to process polymer electrolyte into freestanding film with adequate mechanical strength. Requirement of high cationic transport number rather than anionic is also important in view of the battery performance because concentration gradients caused by the mobility of both cations and anions in the electrolyte arise during discharging, which may result in premature battery failure. Recent advances in nanotechnology have made materials and devices easier to be fabricated at the nanoscale. Nanofibres and nanowires with their huge surface area to volume ratio, about a thousand times higher than that of a human hair, have the potential to significantly improve current technology and find applications in new areas. Nanofibers in particular,