*Article* **High Performance Polymer/Ionic Liquid Thermoplastic Solid Electrolyte Prepared by Solvent Free Processing for Solid State Lithium Metal Batteries**

**Francisco González 1, Pilar Tiemblo 1,\*, Nuria García 1, Oihane Garcia-Calvo 2, Elisabetta Fedeli 2, Andriy Kvasha 2,\* and Idoia Urdampilleta 2**


Received: 6 July 2018; Accepted: 26 July 2018; Published: 2 August 2018

**Abstract:** A polymer/ionic liquid thermoplastic solid electrolyte based on poly(ethylene oxide) (PEO), modified sepiolite (TPGS-S), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ionic liquid is prepared using solvent free extrusion method. Its physical-chemical, electrical, and electrochemical properties are comprehensively studied. The investigated solid electrolyte demonstrates high ionic conductivity together with excellent compatibility with lithium metal electrode. Finally, truly Li-LiFePO4 solid state coin cell with the developed thermoplastic solid electrolyte demonstrates promising electrochemical performance during cycling under 0.2 C/0.5 C protocol at 60 ◦C.

**Keywords:** solid state battery; thermoplastic polymer electrolyte; ionic liquid; sepiolite; inorganic filler
