Description

In recent years, world faces the energy challenges on two main issues. One of them is the electricity production from sustainable energy sources in place of burning fuel. And, another one is shifting the ground transportation toward electric vehicles. For these purposes, energy storage devices such as, batteries, fuel cell, supercapacitors are in demand. Among them, batteries, particularly lithium batteries are the most suitable storage device due to its reasonable energy density, capacity and cycle life. To improve the performance parameters of Li batteries, it is necessary to focus on their components. Present thesis is mainly concerned with developing electrolytes having high thermal stability, wide electrochemical window and sufficient Li+ ion conductivity and cathode materials with high discharge capacity and cyclability for Li batteries. Using polymer electrolytes in place of liquid electrolytes is technologically important for manufacturing and commercializing as they provide safer and flexible Li battery. In polymer electrolytes, polymer poly(ethylene oxide) (PEO) and lithium salt (LiTFSI and/or LiFSI) based systems are suitable electrolytes owing to high conductivity, safety, cyclability and mechanical robustness. But these electrolytes are semi-crystalline in nature which results low segmental motion of polymer chains and causes low ionic conductivity (̱10-6 S/cm) at room temperature. To use them in Li battery, the ionic conductivity of polymer electrolytes should be of the order of 10-5-10-4 S/cm or more which can be achieved in such systems only at temperatures higher than the melting temperature of PEO i.e. when it becomes amorphous. So, for obtaining high ionic conductivity, large amorphous regions of polymer electrolytes are required. There are many techniques to enhance the ionic conductivity and improve electrochemical behavior of PEO-salt systems.