Novel Gel-Polymer Electrolytes for Sodium-Ion Secondary Batteries - An Electrochemical Impedance Spectroscopic Studies

Abstract

Global lithium deposits have been consumed a lot because of the heavy usage of lithium-ion batteries (LIBs) in almost all portable electronic devices and in automobiles. Due to the very limited global lithium resources, the so-called ‘batteries beyond lithium-ion’ such as sodium-ion batteries (SIBs) are becoming popular, particularly in the R&D level. One of the common problems in the commercial level production of SIBs is the synthesis of suitable electrolytes with sufficient ambient temperature ionic conductivities. In this work, a set of novel gel-polymer electrolytes (GPEs) based on poly (methyl methacrylate) (PMMA) host polymer have been synthesized and characterized by electrochemical impedance spectroscopic (EIS), DC polarization and cyclic voltammetric (CV) techniques. The optimized PMMA-NaClO4-EC-DMC GPE composition (10:14:38:38 wt.%) showed an ambient temperature ionic conductivity of 8.4 mS cm-1. Ionic conductivity vs inverse temperature showed Arrhenius behavior with almost same activation energies of 0.16 eV for all the compositions studied. DC polarization test on SS/GPE/SS configuration showed that the best conducting composition is dominantly an ionic conductor (tion ~ 0.998) with negligible electronic conductivity, which is highly desirable to avoid short circuits within the cell. The CV test on best conducting composition revealed that the electrochemical stability window (ESW) of these GPEs is about 4 volts (- 2 to + 2 volts). This optimized composition with highest ambient temperature ionic conductivity and negligible electronic conductivity seems to be a promising candidate for practical applications in sodium-ion secondary batteries.