Investigation of Ion Conduction Mechanism and Relaxation Dynamics in Polymer Nano-Composite Electrolytes

Abstract

Solid-state Li-ion rechargeable batteries are evolving as one of the reliable energy conversion devices due to their higher energy and power density with casing economy. In most of the commercial Li-ion batteries, liquid carbonate based electrolytes are being used. The liquid electrolytes have the disadvantages like leakage, electrode corrosion, limited temperature ranges of operation etc. Therefore, solid polymer electrolytes (SPEs) are widely investigated to replace the conventional liquid electrolytes in these secondary batteries.[1] Though SPEs have various advantages over the liquid counterpart, but its successful realization in practical devices are limited due to their low values of ionic conductivity at ambient and sub-ambient temperatures. SPEs with desired ambient temperature conductivity (~10-3-10-2 Scm-1) have not yet been achieved despite numerous attempts over last four decades by different research groups. In addition, due to complex ion-transport mechanism at molecular level, the ion conduction mechanism in SPEs is an interesting point to explore from fundamental research point of view. A proper understating of ion conduction mechanism will help to increase the ionic conductivity of SPEs for device applications.Broadband dielectric spectroscopy (BDS) is a powerful characterization technique to understand the ion transport mechanism and obtain the information related to ionic and molecular interaction in SPEs. Polymer nano-composite electrolytes (PNCEs) can be considered as one of the simplest SPEs and can provide better insight to ion conduction mechanism at molecular dimensions. PNCEs are prepared with suitable choice of nano-fillers added to polymer salt complex. We have prepared PNCEs using solution casting technique by taking PEO as host polymer, LiCF3SO3 as salt with various fillers like zirconia,[2] titania[3] and modified layered clay[4]. Zirconia acts as neutral filler and it do not actively interact with mobile ions whereas titania acts as Lewis acid and have the capability to weakly attract the free cations. Organo-modified montmorillonite clay is chosen as intercalation filler.Characterization techniques such as XRD, FE-SEM, FTIR and BDS have been adopted to characterize and optimize the materials. The ion conduction mechanism and relaxation dynamics in PNCEs are discussed using different phenomenological approach and theoretical model.[2-5] The concept of coupled ion conduction mechanism is also explained with various formalisms and concept of coupling.