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Effect of Grain Size on the Ionic Conductivity of a Block Copolymer Electrolyte

2014; American Chemical Society; Volume: 47; Issue: 15 Linguagem: Inglês

10.1021/ma501202c

1520-5835

Mahati Chintapalli, X. Chelsea Chen, Jacob L. Thelen, Alexander A. Teran, Xin Wang, Bruce A. Garetz, Nitash P. Balsara,

Membrane Separation and Gas Transport

A systematic study of the dependence of ionic conductivity on the grain size of a lamellar block copolymer electrolyte was performed. A freeze-dried mixture of poly(styrene)-block-poly(ethylene oxide) and lithium bis(trifluoromethylsulfonyl)imide salt was heated in steps from 29 to 116 °C and then cooled back to 29 °C with an annealing time ranging from 30 to 60 min at each temperature. Grain structure and ionic conductivity during these steps were quantified by in situ small-angle X-ray scattering and ac impedance spectroscopy, respectively. Conductivity depends both on grain structure and temperature. A normalization scheme to decouple the dependence of conductivity on temperature and grain structure is described. Ionic conductivity at a given temperature was found to decrease by a factor of 5.2 ± 0.9 as the SAXS measure of grain size increased from 13 to 88 nm. The fact that in the system studied, large, well-formed lamellar grains are less conducting than poorly defined, small grains suggests a new approach for optimizing the transport properties of block copolymer electrolytes. Further work is necessary to confirm the generality of this finding.