Segmental Dynamics Measured by Quasi-Elastic Neutron Scattering and Ion Transport in Chemically Distinct Polymer Electrolytes

Abstract

We investigate the segmental dynamics and ion transport in two chemicallydistinct polymer electrolytes: poly(cyano 2-cyanoethyl acrylate) (PCEA) and poly(ethylene oxide) (PEO), and their mixtures with lithium bis-(trifluoromethane)sulfonimide (LiTFSI) salt. Quasi-elastic neutron scattering experiments reveal slow dynamics in PCEA/LiTFSI relative to that in PEO/LiTFSI, translating to monomeric friction coefficients that are orders of magnitude different. In spite of the enhanced salt dissociation in PCEA due to the presence of polar groups, ion transport is largely dominated by the effect of increased monomeric friction in the pure polymer. Conductivity in these systems is quantified through a simple expression combining salt dissociation, the monomeric friction in the pure polymer, and the effect of added salt on the monomeric friction.

Polymer Dynamics in Block Copolymer Electrolytes Detected by Neutron Spin Echo

“…In conclusion, the effect of added salt on the polymer dynamics of a nanostructured block copolymer electrolyte are investigated using NSE on the 0.1–100 ns time scale and analyzed using the Rouse model at short times ( t ≤ 10 ns) and the reptation model at long times ( t ≥ 50 ns). The effect of salt concentration on the segmental dynamics in the Rouse regime matches the results of previous experiments on homopolymer electrolytes: monomeric friction increases with increasing salt concentration. − In the reptation regime, the tube diameter decreases with increasing salt concentration. We attribute this trend to temporary cross-links between neighboring chains arising from Li + ion coordination.…”

“…3,[7][8][9][10] In these cases, the translation of ions can be accommodated by segmental relaxation of the polymer chains. 11,12,21,[13][14][15][16][17][18][19][20] Thus, ionic conductivity of a well-studied polymer electrolyte, a mixture of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt measured by ac impedance spectroscopy, can be explained entirely by the segmental relaxation quantified by quasi-elastic neutron scattering (QENS). 14 To our knowledge, no attempt has been made to study the relaxation processes that govern polymer electrolytes under large applied potentials.…”

“…The effect of salt concentration on the segmental dynamics in the Rouse regime matches the results of previous experiments on homopolymer electrolytes: monomeric friction increases with increasing salt concentration. [11][12][13][14][15]21 In the reptation regime, the tube diameter decreases with increasing salt concentration. We attribute this trend to temporary crosslinks between neighboring chains arising from Li + ion coordination.…”

“…A popular approach for characterizing ion transport in electrolytes is ac impedance spectroscopy, which reflects the oscillation of ions in response to a small ac potential. ,, Another popular approach is pulse-field gradient NMR, wherein the Brownian motion of ions is quantified in the absence of an applied potential. ,− In these cases, the translation of ions can be accommodated by segmental relaxation of the polymer chains. − Thus, ionic conductivity of a well-studied polymer electrolyte, a mixture of poly­(ethylene oxide) (PEO) and lithium bis­(trifluoromethanesulfonyl)­imide (LiTFSI) salt measured by ac impedance spectroscopy, can be explained entirely by the segmental relaxation quantified by quasi-elastic neutron scattering (QENS) . To our knowledge, no attempt has been made to study the relaxation processes that govern polymer electrolytes under large applied potentials.…”

Accelerating Battery Characterization Using Neutron and Synchrotron Techniques: Toward a Multi‐Modal and Multi‐Scale Standardized Experimental Workflow

“…Quasi‐elastic neutron scattering (QENS) is unique in providing a direct observation of ionic conduction mechanism on timescales ranging from picoseconds through to microseconds, yielding key information on the geometrical character of the ionic motion, distinguishing for example between continuous, liquid‐like diffusion, and discrete hopping between specific sites. [ 41 ]…”