Decoding Polymer Architecture Effect on Ion Clustering, Chain Dynamics, and Ionic Conductivity in Polymer Electrolytes

Abstract

Poly(ethylene oxide) (PEO)-based polymer electrolytes are a promising class of materials for use in lithium-ion batteries due to their high ionic conductivity and flexibility. In this study, the effects of polymer architecture including linear, star, and hyperbranched and salt (lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI)) concentration on the glass transition (T g ), microstructure, phase diagram, free volume, and bulk viscosity, all of which play a significant role in determining the ionic conductivity of the electrolyte, have been systematically studied for PEO-based polymer electrolytes. The branching of PEO widens the liquid phase toward lower salt concentrations, suggesting decreased crystallization and improved ion coordination. At high salt loadings, ion clustering is common for all electrolytes, yet the cluster size and distribution appear to be strongly architecture-dependent. Also, the ionic conductivity is maximized at a salt concentration of [Li/EO ≈ 0.085] for all architectures, and the highly branched polymers displayed as much as three times higher ionic conductivity (with respect to the linear analogue) for the same total molar mass. The architecture-dependent ionic conductivity is attributed to the enhanced free volume measured by positron annihilation lifetime spectroscopy. Interestingly, despite the strong architecture dependence of ionic conductivity, the salt addition in the highly branched architectures results in accelerated yet similar monomeric friction coefficients for these polymers, offering significant potential toward decoupling of conductivity from segmental dynamics of polymer electrolytes, leading to outstanding battery performance.

Single Ion Conducting Hairy Nanoparticle Additive to Improve Cycling Stability of Solid Polymer Electrolytes

“…The literature indicates that PEO crystallizes into a lamellar structure, 26−28 and PEO/ LiTFSI blends maintain the semicrystalline properties of PEO up to molar ratio of Li/EO = 0.085. 29 This observation is consistent with our study of PEO-LiTFSI blend with a molar ratio Li/EO = 0.051, where a lamellar structure is manifested in a broad first-order peak followed by second-order reflections (Figure 1A). The spectra of Hairy and PolyIL PCs resemble spectral features of PEO-LiTFSI, which is indicative of lamellar morphology.…”

“…The morphology of the composites was examined with SAXS, and the scattering spectra and their corresponding fitting based on the model detailed in the Supporting Information are shown in Figure A. The literature indicates that PEO crystallizes into a lamellar structure, − and PEO/LiTFSI blends maintain the semicrystalline properties of PEO up to molar ratio of Li/EO = 0.085 . This observation is consistent with our study of PEO-LiTFSI blend with a molar ratio Li/EO = 0.051, where a lamellar structure is manifested in a broad first-order peak followed by second-order reflections (Figure A).…”

Salt Effects on the Mechanical Properties of Ionic Conductive Polymer: A Molecular Dynamics Study

“…(a) Modulus of the frequency-dependent viscosity |η*(ω)|and (b) G ″(ω) /ω for the neat PEO and PEO-LiTFSI systems at different concentrations and at temperature T – T g ≈ 120 K. (b) Comparing the equilibrium viscosity η computed from eqs and with experimental values , for PEO-LiTFSI systems as a function of salt concentration.…”

Polymeric Electrolytes for Solid‐state Lithium Ion Batteries: Structure Design, Electrochemical Properties and Cell Performances

“…In crystalline SPEs, meticulous control over grafting density alleviates side-chain crystallization, thus enhancing ion conductivity within the branched polymer matrix. Furthermore, Senses [138] conducted a comprehensive exploration of the impact of linear, star-shaped, and hyperbranched structures on polymer properties such as T g , phase diagrams, and free volume, all of which substantially influence ion conductivity in SPEs. Their findings emphasize the substantial dependency of ion conductivity on polymer structure.…”