Improved Li⁺ Transport in Polyacetal Electrolytes: Conductivity and Current Fraction in a Series of Polymers

Abstract

Polymer electrolytes mitigate safety concerns surrounding flammable liquid electrolytes in lithium-ion batteries. Poly(ethylene oxide) (PEO) electrolytes demonstrate viable conductivity values (∼1 × 10 −3 S/ cm) at elevated temperatures (>70 °C) but a relatively low Li + current fraction (≤0.2) because strong Li + coordination inhibits cation mobility. We have developed a series of polyacetal electrolytes by systematically varying methylene oxide (MO) and ethylene oxide (EO) units in the polymer backbone. These materials maintain high oxygen-to-carbon ratios like PEO but offer improved ion transport, revealing trends of decreasing conductivity and increasing current fraction with respect to polymer composition. In particular, the increasing current fraction measured via the Bruce−Vincent method suggests that MO units improve Li + mobility relative to anion mobility. We calculate an overall efficacy (product of conductivity and current fraction) for each polymer/salt composition and identify two polymersP(EO-MO) and P(EO-2MO)that outperform PEO at high and low salt concentrations, respectively.

Crosslinked xylose-based polyester as a bio-derived and degradable solid polymer electrolyte for Li+-ion conduction

“…Amongst the various polymer chemistries investigated for SPE application, those comprising of polyethylene oxide (PEO) with various lithium salts have undoubtedly received the most interest, however recent studies of similar polyethers and polyacetals have also been reported by Balsara and Coates. 9–13 Despite high ionic conductivity ( ca. 10 −3 S cm −1 at 70 °C) above the melting temperature of PEO, poor room temperature performance, high crystallinity and low lithium transference numbers (typically around 0.2) of PEO-based SPEs remain a limitation to their practical implementation.…”

Electric-Field-Induced Spatially Dynamic Heterogeneity of Solvent Motion and Cation Transference in Electrolytes

“…), defined as the fraction of ionic current carried by the cation relative to the solvent velocity in an electrolyte of uniform composition [2]. Recognition of the importance of this transport parameter dates back to Hittorf [3,4]; more recent work has emphasized the relevance of the cation transference number to the electrochemical efficacy of the electrolyte under fast charging conditions [8][9][10] and circumstances that lead to lithium dendrite growth [11,12]. Newman's concentrated solution theory can be used to relate 𝑡 ! "…”

A Facile and Unprecedented Route to a Library of Thermostable Formaldehyde‐Derived Polyesters: Highly Active and Selective Copolymerization of Cyclic Acetals and Anhydrides

“…Consequently, we envisioned that the cationic copolymerization of cyclic acetals with anhydrides would be a novel way to produce polyesters. Of note, we can readily produce cyclic acetals on a large scale using common industrial feedstocks of formaldehyde and diols [39] …”