A comparative study on the influence of the polymeric host for the operation of all-solid-state batteries at different temperatures

Abstract

Solid Polymer Electrolytes (SPE) are critical components to develop safe, high energy density all solid-state lithium metal batteries (ASSB), providing favorable mechanical properties and good stability vs Li-metal. Typically used poly(ethylene oxide) (PEO) based electrolytes do not allow cycling of all solid-state cells at room temperature due to the crystallization of PEO hindering the ionic transport. Increasing the ionic conductivity of SPE at lower temperature is then mandatory. This study addresses the challenge thanks to the use of Polymerized ionic liquid (PIL), poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PDADMAT) as polymeric host for producing SPE. Mixtures of PDADMAT and PEO with tetraglyme Li salt IL, LiG4TFSI, are prepared and their electrochemical properties in lithium metal batteries investigated. Through composition optimization, membranes containing 66 wt % of LiG4TFSI were selected as the best compromise in term of conduction properties (above 10−4 S/cm at room temperature), transference number of ca. 0.4 and mechanical behavior. All-solid-state cells prepared using PDADMAT-based membranes were able to cycle at 60 °C and room temperature up to 0.425 mA/cm2 current densities whereas POE-based cells could only sustain 60 °C cycling. The study underlines the benefit of using IL and PIL as components of SPE for the operation of high performance ASSB at room temperature.