Versatile solid polymer electrolytes from clickable poly(glycidyl propargyl ether) for lithium metal batteries

Abstract

We present three new graft copolymers for the application as solid polymer electrolytes (SPEs) in solvent-free, all solid-state lithium metal batteries (LMBs), based on the clickable poly (glycidyl propargyl ether) platform. These fully amorphous polymers consist of an all-ether polymer backbone and different additional Li+-coordinating oxo-functionalities - diester, carbonate and phosphate ester - in the attached sidechain. We aim to address the fundamental question on the influence of Li+-coordination in such doubly functionalized systems having competing Li+-coordination functional groups. We prepared polymer nanocomposite SPEs based on these novel polymers mixed with a highly-dissociating lithium salt (LiTFSI) and TiO2 nanofillers, which improve the electrolyte-electrode compatibility. We perform an extensive and comparative investigation in terms of physicochemical and electrochemical properties including ionic conductivity, lithium transference number, lithium plating and stripping as well as the fabrication and cycling of LMBs utilizing lithium iron phosphate (LFP) cathodes. Thermal characterization is coupled with temperature-dependent ionic conductivity measurements and detailed IR spectroscopy to understand the mechanistic properties and selectivity of the Li+ coordination and conduction. Two of the nanocomposite SPEs show efficient battery cycling with initial capacities of ca. 150 mAh g−1 and a capacity retention of ca. 70–80 % after 100 cycles.