Lorena Grundy, University of California, Berkeley
Abstract:
Block copolymer electrolytes that microphase separate into mechanically rigid and ion-conducting domains are promising materials for lithium metal batteries. We study a block copolymer electrolyte composed of polystyrene-block-poly(ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) which, under equilibrium conditions, exhibits a hexagonally packed cylindrical (HEX) morphology at low salt concentrations and a body-centered cubic spherical (BCC) morphology at high salt concentrations. The limiting current, which causes the cell potential to diverge exponentially if exceeded, thus limiting battery charging rates, is usually reached when the salt concentration at the negative electrode approaches zero due to concentration polarization. We use in situ X-ray scattering and absorption to study the salt concentration and morphology profiles of our SEO/LiTFSI electrolyte, which exhibits a BCC morphology at equilibrium, as a function of position and time during polarization. We expected to obtain a HEX morphology near the negative electrode as the limiting current is approached and the salt concentration at the negative electrode approaches zero. Instead, we find that the cell potential diverges when the salt concentration at this electrode approaches the concentration at the BCC/HEX boundary at high current densities. The maximum current that can be carried by our electrolyte is thus not limited by the lack of salt at the negative electrode. Instead, it appears to be related to a phase transition that occurs readily in equilibrated samples but is inaccessible in a polarized cell. This illustrates the valuable insights provided by simultaneous electrochemical and X-ray scattering and absorption techniques, and opens new avenues for future exploration into the behavior of block copolymer electrolytes.
Poster Session Link: https://gather.town/invite?token=0pEoq7VP
If you have any questions for the presenter, please contact them via email: lgrundy@berkeley.edu