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Published October 12, 2010 | public
Journal Article

Thermodynamic Properties of Block Copolymer Electrolytes Containing Imidazolium and Lithium Salts


We report on the thermal properties, phase behavior, and thermodynamics of a series of polystyrene-block-poly(ethylene oxide) copolymers (SEO) mixed with the ionic species Li[N(SO_(2)CF_3)_2] (LiTFSI), imidazolium TFSI (ImTFSI), and an equimolar mixture of LiTFSI and ImTFSI (Mix). Differential scanning calorimetric scans reveal similar thermal behavior of SEO/LiTFSI and SEO/ImTFSI at the same salt concentrations. Phase behavior and thermodynamics were determined using a combination of small-angle X-ray scattering and birefringence. The thermodynamics of our mixtures can be mapped on to the theory of neat block copolymer phase behavior provided the Flory−Huggins interaction parameter, χ, between the blocks is replaced by an effective χ (χ_(eff)) that increases linearly with salt concentration. The phase behavior and the value of m, the slope of the χ_(eff) versus salt concentration data, were similar for SEO/LiTFSI, SEO/ImTFSI, and SEO/Mix blends. The theory developed by Wang [ J. Phys. Chem. B. 2008, 41, 16205] provides a basis for understanding the fundamental underpinnings of the measured value of m. We compare our experimental results with the predictions of this theory with no adjustable parameters.

Additional Information

© 2010 American Chemical Society. Received June 21, 2010; Revised Manuscript Received August 25, 2010. Publication Date (Web): September 13, 2010. This work was supported by the National Science Foundation (DMR-0966662, CBET-0965812, and CBET-0966632) and the Batteries for Advanced Transportation Technologies (BATT) Program, supported by the U.S. Department of Energy FreedomCAR and Vehicle Technologies Program. N.S.W. was supported by a National Science Foundation Graduate Research Fellowship. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy, under Contract No. DE-AC02-05CH11231. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. We thank Shrayesh Patel for helpful discussions and Ariel Tsui for experimental help.

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