Journal
CHEMISTRY OF MATERIALS
Volume 24, Issue 12, Pages 2316-2323Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm3005387
Keywords
ionomer; tetraphenyl borate; electrode polarization; carrier activation energy and mobility
Funding
- Department of Energy [BES-DE-FG02-07ER46409]
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Three borate monomers: lithium triphenylstyryl borate (B1), a variant with three ethylene oxides between the vinyl and the borate (B2) and a third with perfluorinated phenyl rings (B3) were synthesized and used to prepare polysiloxane ionomers based on cyclic carbonates via hydrosilylation. B1 ion content variations show maximum 25 degrees C conductivity at 8 mol %, reflecting a trade-off between carrier density and glass transition temperature (T-g) increase. Ethylene oxide spacers (B2) lower T-g, and increase the dielectric constant, both raising conductivity. Perfluorinating the four phenyl rings (B3) lowers the ion association energy, as anticipated by ab initio estimations. This increases conductivity, a direct result of 3 times higher measured carrier density. The similar to 9 kJ/mol activation energy of simultaneously conducting ions is less than half that of ionomers with either sulfonate or bis(trifluoromethanesulfonyl) imide anions, suggesting that ionomers with weak-binding borate anions may provide a pathway to useful single-ion Li+ conductors, if their T-g can be lowered.
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