Salt-Concentration Dependence of the Glass Transition Temperature in PEO–NaI and PEO–LiTFSI Polymer Electrolytes

Abstract

We measured glass transition temperatures T g as a function of the salt concentration in polymer electrolyte systems consisting of poly(ethylene oxide) (PEO) complexed either with sodium iodide (NaI) or lithium bis(trifluorosulfonylimide) (LiTFSI). At homologous compositions, T g of PEO–NaI is found to be generally larger than that of LiTFSI. The present T g values are markedly higher than previously reported reference data. Also the observed nonlinear concentration dependence differs from earlier studies. These findings are tentatively attributed to the more stringent preparation and measuring conditions maintained in the present work, thereby keeping organic solvent residues and water contamination at low levels. Also the high molecular weight of the polymer may have some influence. The measurements were performed by differential scanning calorimetry after quenching from the melt. We find that ex situ immersion quenching in liquid nitrogen leads to lower degrees of crystallinity than in situ quenching in the calorimeter environment. In addition, the strong decrease of the crystallinity with increasing salt content gives rise to pronounced steps in the heat capacity near T g for the more concentrated electrolytes.

A new solid polymer electrolyte incorporating Li10GeP2S12 into a polyethylene oxide matrix for all-solid-state lithium batteries

“…(3), where DH m is the melting enthalpy of electrolyte, and DH PEO is the value of 196.4 J g À1 for PEO perfect crystal reported in literature [20] for the melting enthalpy of 100% crystalline PEO, and f PEO is the PEO weight fraction of the electrolyte sample.…”

Self‐Standing Highly Conductive Solid Electrolytes Based on Block Copolymers for Rechargeable All‐Solid‐State Lithium‐Metal Batteries

“…Trying to overcome above‐mentioned drawbacks of PEO‐based SPEs, tremendous efforts have been devoted to the design of non‐crystalline and low T g polymer matrices, such as structural alteration by random, comb, and/or block copolymerization . Block copolymer‐based SPEs are a promising solution that combines both good mechanical properties and ionic conductivity .…”

Identification of relaxation processes in pure polyethylene oxide (PEO) films by the dielectric permittivity and electric modulus formalisms

“…Polyethylene oxide is a nontoxic semiconducting polymer of complex molecular structure {H − [O − CH 2 − CH 2 ] n − OH} with molecular weight M w =18.02 + 44.05 n >10 5 g/mol, where n is the number of repeated molecular chain‐like units of identical monomers. The pure PEO has melting point T m <72 ° C (345 K), crystallization temperature T c ≲60 ° C (333 K), and low glass transition temperature T g (≳ − 58 ° C ≅ 215 K), depending on its molecular weight, and possesses strong solvating ability for many metal ions, including Li . Besides its ability to dissolve inorganic lithium‐ion salts, PEO polymer is highly soluble in water and organic solvents (ethanol, methanol, and toluene), so it can be fabricated in the form of solid films by various solvent‐evaporation coating methods .…”