Carbonate swollen lithiated Nafion electrolyte for quasi-solid-state lithium-sulfur batteries

Abstract

A solid-state polymer electrolyte (SPE) could be a viable alternative in order to reduce polysulfide mobility and to mitigate the shuttle effect in lithium-sulfur batteries. In this work, single lithium-ion conducting solid polymer electrolytes (SLIC-SPEs) based on a lithiated Nafion membrane have been prepared and characterized for such a purpose. In the search for organic aprotic swelling solvents that do not cause instability or phase separation problems in the membrane and are suitable for use in lithium-sulfur batteries, only a few were found. They included a mixture of ethylene carbonate (EC) and propylene carbonate (PC), and glyme molecules that did not cause undesirable leaching of the solvent during thermal cycling. A thorough and systematic study of lithium-ion transport was conducted on the swollen membranes by pulsed-field gradient nuclear magnetic resonance (PFG-NMR) and electrochemical impedance spectroscopy (EIS), while the mechanical properties have been tested by dynamic mechanical analysis (DMA). A combination with gas phase infiltrated sulfur-carbon composite cathodes did not only enable the use of carbonate-based solvents in a quasi-solid-state lithium sulfur full cell, but also allow almost complete utilization of the active material without the need for liquid electrolyte additions. Carbonate plasticized Nafion electrolyte improves safety as it is non-toxic, high-boiling and non-flammable. The material combination of a sulfur embedded cathode and ionomer/EC/PC thus opens the way to applications in the field of thin, mechanically flexible and safe high-energy batteries for smart textiles.