Influence of Dielectric Constant on Ionic Transport in Polyether-Based Electrolytes

Abstract

We use all-atom molecular dynamics simulations to study the effect of polymer polarity, as quantified by the dielectric constant, on the transport properties of lithium bis­(trifluoromethylsulfonyl)­imide (LiTFSI) doped polyethers. Our results indicate that increasing the host dielectric constant leads to a decrease in ionic cluster sizes and reduction in correlated motion of oppositely charged ions. This causes the ionic conductivity to more closely approach the Nernst-Einstein limit in which ionic conductivity is only limited by the diffusivities of Li+ and TFSI–. We compare our results to recent experimental observations which demonstrate similar qualitative trends in host polarity.

Multivalent ion conduction in solid polymer systems

“…8 Experimental and theoretical studies suggest that increasing the dielectric constant of the polymer environment can reduce ionion interactions by improving screening between ion pairs, thus leading to enhanced dissociation and ion mobility. [18][19] Ion-polymer interactions also play a significant role in ion mobility. Polymer solvation sites, which stabilize the dissociation of a salt into its respective ions, generally interact more strongly with cationic species, which are also the ions of interest for most applications.…”

Lithium and magnesium polymeric electrolytes prepared using poly(glycidyl ether)-based polymers with short grafted chains

“…Interestingly, the conductivity did not scale monotonically with the T g of the polymers suggesting additional contributions playing a major role in the ion mobility. Follow-up studies reported by Wheatle et al 29,30 confirmed the relevance of the polymer backbone polarity by comparing computational and experimental results obtained for different structures 29 and by claiming the existence of an optimal compromise between ion solvation and segmental mobility that must be taken into account in designing novel PEs. 30 Using different heteroatoms than oxygen in the polymer structure is a straightforward method to modify both chain mobility and polarity.…”

“…In this perspective, poly(ether) s 17,21,22 and poly(vinyl alcohol)s 23 and their derivatives have been attempted, but the coordination of magnesium dications with the oxygen atoms is stronger than that of lithium, reducing the overall conductivity of the resulting complexes and increasing the related T g . [24][25][26] Despite the fact that segmental mobility is considered to be one of the most important factors for high ionic conductivity, an increasing number of studies have highlighted that T g is not always a vital parameter [27][28][29][30][31][32][33] and also other possible transport mechanisms can contribute to ion mobility in the matrix. [31][32][33][34][35] In the Salt in Polymer Electrolyte (SIPE) and dilute regimes, the interplay between chain polarity and stiffness is relevant, controlling the solvation mechanisms of the salts and their mobility through the polymer matrices.…”

“…[31][32][33][34][35] In the Salt in Polymer Electrolyte (SIPE) and dilute regimes, the interplay between chain polarity and stiffness is relevant, controlling the solvation mechanisms of the salts and their mobility through the polymer matrices. 29,30,36 A class of poly(allyl glycidyl)ethers (PAGEs) proposed by Barteau et al 28 offered the opportunity to investigate the effect of several structural parameters on the resulting conductivity of the lithium-complexes. Interestingly, the conductivity did not scale monotonically with the T g of the polymers suggesting additional contributions playing a major role in the ion mobility.…”

Re‐weighted random series path integral simulations of molecular clusters: Applications to lithium solvated by a mixed Stockmayer cluster

“…Even though the body of knowledge gathered to date on clusters is vast, we find surprisingly little work dedicated to the study of Stockmayer and ion‐Stockmayer clusters in the literature. The present goals are of fundamental importance for the research and development of lithium ion batteries, as a practical application. Lithium ion batteries are complex bulk systems, and their direct simulations will likely require more realistic models to extend the scope of the present investigation.…”