Effect of Polymer Polarity on Ion Transport: A Competition between Ion Aggregation and Polymer Segmental Dynamics

Abstract

In this work, we use computer simulations to demonstrate that there may be limits to which polymer polarity alone can be used to influence the ionic conductivity of salt-doped polymer electrolytes. Specifically, we use coarse-grained molecular dynamics simulations to probe the effect of the polarity of the polymer electrolyte upon ion mobilities and conductivities of dissolved salts. At low polymer polarities, increasing the polymer dielectric constant reduces ionic aggregation and the resultant correlated ionic motion, and increases the ionic conductivity. At higher polymer polarities, polymer−polymer and polymer−ion interactions slows polymer segmental dynamics, leading to a reduction in the conductivity of the electrolyte. As a consequence, ionic conductivity achieves an optimum at an intermediate polymer polarity.

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.…”

“…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. Specifically, the presence of sulfur heteroatoms in combination with oxygen has been proved to give encouraging results for lithium transport, even though crystallinity is not prevented.…”

“…The differences in the trends between the conductivities of the LiTFSI and LiCl complexes may also reflect the differences in the interactions of the two anions with the host polymers. 30,56,58 The strong dipole interaction of the sulfone group plays a major role in the conductivity of PEsulfoPGE, outperforming even PAGE which has a lower T g of about 40°C.…”

“…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.…”