| 초록 |
The effect of nanoscale structure on the mechanical and electrical properties of lamellar block copolymers doped with lithium salts is studied. Ion transport is restricted to one of the microphases while the other microphase is a hard insulator. We demonstrate that electrolytes with high conductivity and shear modulus are obtained by this approach. We focus on lamellar samples with poly(ethylene oxide) (PEO) volume fractions, Φ, ranging from 0.38 to 0.55, and PEO block molecular weights, MPEO, ranging from16.3 to 98.1 kg/mol. The low frequency storage modulus (G') modulus at 90 ºC increases with increasing MPEO, from about 4x105 to 5x107 Pa. Surprisingly, the conductivity of the SEO/salt mixtures, σ, also increases with increasing MPEO, from 6.2x10-5 to 3.6x10-4 S/cm at 90 °C. We compare σwith the conductivity of pure PEO/salt mixtures, σPEO, and find that σ/ΦσPEO of our highest molecular weight sample is close to the theoretical upper limit for randomly oriented grains (σ/ΦσPEO = 2/3). In order to determine the role of structure on the ionic conductivity of these materials, we perform various transmission electron microscopy (TEM) experiments. Three-dimensional reconstructions provide important structural information regarding the manner in which the conductive phase percolates through the copolymer electrolyte. Energy-filtered electron microscopy allows for the direct imaging of lithium. Current efforts are focused on using these TEM experiments to determine the structure-conductivity relationships of block copolymer battery electrolytes. The applicability of these materials as dry electrolytes in lithium ion batteries will be discussed. |
