A Precision Polyanion for High Performance Lithium-Ion Transport in Polymer Blend Electrolytes

Abstract

A novel precision single ion conductor with an N-((trifluoromethyl)sulfonyl)phenylsulfonimide lithium salt covalently bound to every fifth carbon of a polyethylene backbone, p5PhTFSI-Li, was synthesized via post polymerization modification. The conversion to a trifluoromethanesulfonimide (TFSI) anion from the parent polymer bearing a phenylsulfonate anion was highly efficient (~90%) as determined by 19F-NMR analysis and corroborated through other spectroscopic methods. The bulky and flexible TFSI anion led to a reduced and observable glass transition temperature of ~199 °C and an improved thermal stability up to ~375 °C. Blending of p5PhTFSI-Li with poly(ethylene oxide) at various compositions was performed to investigate electrochemical performance and transference numbers with respect to the lithium electrode using a combination of impedance and polarization methods. At 90 °C, this system displayed high conductivity up to 2.00 X 10-4 S cm-1 and transference numbers were near unity independent of temperature, making this system highly competitive with other polyanion/polyether blend electrolytes. Investigations into the complex miscibility and phase behavior of these blends at various compositions was also probed by a combination of microscopy and differential scanning calorimetry.