Self-standing single lithium ion conductor polymer network with pendant trifluoromethanesulfonylimide groups: Li+ diffusion coefficients from PFGSTE NMR

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Solid electrolyte materials have the potential to improve performance and safety characteristics of batteries by replacing conventional solvent-based electrolytes. For this purpose, new candidate single ion conductor self-standing networks were synthesized with trifluoromethane-sulfonylimide (TFSI) lithium salt based monomer using poly(ethyleneglycol) dimethacrylate (PEGDM 750) as crosslinker. The highest ionic conductivity was 3.4×10−7Scm−1 at 30°C in the dry state. Thermal and mechanical analyses showed good thermal stability up to 190°C and rubbery-like properties at ambient temperature. A direct relationship between ionic conductivity and glassy or rubbery state of the membranes was found. Vogel–Tammann–Fulcher behavior was observed in the dry state which is consistent with a lithium conductivity correlated with polymer chain mobility. By swelling the network in propylene carbonate, a self-standing electrolyte gel could be obtained with an ionic conductivity as high as 1×10−4Scm−1 at 30°C. The individual diffusion coefficients of mobile species in the material (19F and 7Li) were measured and quantified using pulsed-field gradient nuclear magnetic resonance (PFG-NMR). Diffusion coefficients for the most mobile components of the lithium cations and fluorinated anions at 100°C in dry membranes have been found to be 3.4×10−8cm2s−1 and 2.1×10−8cm2s−1 respectively.