(402c) Investigating the Effect of Salt on Segmental Dynamics in Block Copolymer Electrolytes for Lithium Batteries

Block copolymers have been studied for use in lithium metal solid-state batteries due to their ability to decouple ion transport and mechanical properties. While it is well known that the salt preferentially segregates into the conducting block, and that the motion of salt molecules is coupled to that of the polymer segments that solvate the ions, many questions about the nature of this coupling remain unanswered. We will present the results of neutron spin-echo (NSE) experiments that elucidate the nature of this coupling. The sample used was a mixture of a protonated and deuterated polystyrene-block-poly(ethylene oxide) doped with a lithium salt. The isotopic labeling allowed for only the dynamics of the ion-containing block, poly(ethylene oxide), to be measured. The mixture composition was chosen to maximize the scattered intensity in the NSE experiment at scattering vectors, q, ranging from 0.11 to 0.25 Å^-1. We quantified the dynamics in this window (corresponding to length scales of about 5 nm) by comparing the data to predictions based on the standard tube model of de Gennes and Edwards. The tube shrinks with added salt and the segments slow down due to this. There is a direct relationship between segmental dynamics measured on the monomer length scale and ion transport under an applied field on macroscopic length scales.