(193av) Structural Dynamics of Strongly Segregated Block Co-polymer Electrolytes

Authors: 
Iyiola, O., Florida State University
Oparaji, O., Florida State University
Ramakrishnan, S., FAMU-FSU College of Engineering
Sandy, A., Argonne National Laboratory
Narayanan, S., Argonne National Laboratory
Hallinan, D. Jr., FAMU-FSU College of Engineering
The push for clean energy has long sparked technological advances in energy storage devices such as batteries. Lithium Ion batteries (LIBs) have been at the forefront with multiple successes and intermittent failures majorly due to safety. Solid state (polymer) electrolytes address these safety concerns. Polymer based electrolytes comprising poly (styrene-block-oxyethylene) (SEO) have shown to be very stable and a good host for Lithium based salts such as lithium bistrifluoromethanesulfonimide (LiTFSI) but show low ionic conductivity and loss of stability during cycling because of the inherent relaxation processes as well as the polymer dynamics have been the limiting factors. One way to understand the structure and dynamics is via the use of X-ray Photon Correlation Spectroscopy (XPCS). XPCS is a novel technique that can correlate the electron density contrast and thus measure dynamics on time scales between 10−4 and 104 s. Structural dynamics results from XPCS showed hyperdiffusive motion for various lithium salt concentrations and at different temperatures which is synonymous to soft glassy materials. This behavior is attributed to cooperative dynamics. Rheological studies of similar samples showed the shear modulus decreased with increasing salt concentration and increasing temperature. The entanglement relaxation from rheological measurements followed Vogel−Fulcher−Tammann behavior. Comparing the times scales for both the structural and entanglement relaxation, we found that the former was slower than the latter at temperatures above the glass transition temperature, but were approximately equal at Tg irrespective of salt concentration. These finding lead us to conclude that salt affects the morphology but not the dynamics of strongly segregated polymers.