Effect of molecular weight on the mechanical and electrical properties of block copolymer electrolytes.

The relationship between ionic conductivity, morphology, and rheological properties of polystyrene-block-poly(ethylene oxide) copolymers (SEO) doped with a lithium salt, Li[N(SO2CF3)(2)], is elucidated. We focus on lamellar samples with poly(ethylene oxide) (PEO) volume fractions, phi, ranging from 0.38 to 0.55, and PEO block molecular weights, M-PEO, ranging from 16 to 98 kg/mol. The low-frequency storage modulus (G') at 90 degrees C increases with increasing M-PEO from about 4 x 10(5) to 5 x 10(7) Pa. Surprisingly, the conductivity of the SEO/salt mixtures with the molar ratio of Li to ethylene oxide moieties of 0.02 sigma, also increases with increasing M-PEO, from 6.2 x 10(-5) to 3.6 x 10(-4) S/cm at 90 degrees C. We compare sigma with the conductivity of pure PEO/salt mixtures, sigma(PEO), and find that sigma/[phi sigma(PEO)] of our highest molecular weight sample is close to 0.67, the theoretical upper limit for transport through randomly oriented lamellar grains. © 2007, American Chemical Society

Keywords

Lithium, Grain boundaries, Electrolytes, Copolymers, Self-diffusion, Ionic conductivity, Solid state physics

Citation

Singh, M., Odusanya, O., Wilmes, G. M., Eitouni, H. B., Gomez, E. D., Patel, A. J., Chen, V. L., Park, M. J., Fragouli, P., Latrou, H., Hadjichristidis, N., Cookson, D. J., & Balsara, N. P. (2007). Effect of molecular weight on the mechanical and electrical properties of block copolymer electrolytes. Macromolecules, 40(13), 4578-4585. doi:10.1021/ma0629541