Sodium-Ion Polymer Batteries Assembled with Composite Gel Polymer Electrolytes

Abstract

Rechargeable sodium-ion batteries have become the promising energy storage system due to their high energy density, long cycle life and lower cost. However, safety issues surrounding these batteries must be addressed before they can be widely utilized in large-scale applications such as electric vehicles and grid-scale energy storage devices. Therefore, the quest for safer and more reliable electrolyte system is urgent and polymer electrolytes are promising candidates in this regard. However, they suffer from poor thermal stability and mechanical properties. In order to obtain the gel polymer electrolytes with improved thermal and mechanical properties, ceramic fillers such as SiO2, Al2O3, TiO2 and BaTiO3 have been incorporated into host polymers. In these composite gel polymer electrolytes, the ceramic particles promote electrochemical properties of the polymer electrolytes through physical interactions without directly contributing to the lithium ion transport process. As reported in our previous studies, the ionic conductivity of gel polymer electrolyte was improved by using ceramic fillers covered with poly(styrene sulfonated lithium)(PLSS) containing lithium cation end group [1,2,3]. It is of our interest to synthesize and introduce inorganic materials containing dissociative sodium ions in the electrolyte of sodium-ion batteries to improve the ionic conductivity, thermal stability and mechanical property. In this study, we prepared composite gel polymer electrolytes based on core-shell structured SiO2 nanoparticles containing dissociative sodium ions. The SiO2 particles have unique core-shell morphology with a thin layer of poly(sodium 4-styrene sulfonate) surrounding nano-sized SiO2core particle. The composite gel polymer electrolyte exhibited high ionic conductivity and good mechanical strength. The prepared gel polymer electrolytes were used to assemble sodium-ion polymer batteries, and their cycling performances were evaluated.