Future electrochemical power sources require new electrolytes to adapt to disruptive changes in the basic working chemistry, such as moving from Li ion to Na ion, or to Li metal electrodes. We highlight several recent collaborative activities on electrolytes in our group (i) Na ion; (ii) Li metal polymer. Low molecular mass polyethers (i.e. glymes), serve as useful models for investigating ion/polymer and ion/ion interactions in higher molecular mass polyethers, i.e. PEO. Glymes have also garnered recent attention as attractive solvents for use in lithium metal and lithium sulfur batteries. We have undertaken a comprehensive study of variable chain length glymes,containing lithium salts or sodium salts.. NMR methods employed include (i) natural abundance 17O, (ii) pulsed field gradient diffusion of solvent (through 1H), cation (7Li or 23Na), and anion (19F). In lithium salt glyme complexes, correlations between both solvent and anion 17O chemical shifts and chain length yield insight into solvation structures and ion pairing tendencies which are supported by the diffusion measurements. Similar behavior is observed in the corresponding sodium solutions, with some differences attributed to the larger ionic radius of Na+. This work has most recently been extended to NaPF6 – glyme solutions being developed for supercapacitor applications. We next discuss a novel solvent-free solid polymer with room temperature ionic conductivity exceeding 1 mS/cm, is non-flammable, has attractive mechanical properties for lithium dendrite suppression, and is compatible with Li metal as well as a wide variety of cathodes. It is based on semicrystalline polyphenylene sulfide and Li salts familiar to the battery community. The ionic transport mechanism is decoupled from polymer host motion, and NMR measurements reveal Li self-diffusion coefficients at room temperature that are the highest reported in any known solid, with a Li+ transport number greater than 0.6.

Liquid and solid state NMR investigations of low MW Polyether and non-polyether polymer electrolytes for supercapacitor and battery applications

255th National Meeting (2018)

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