The Role of Backbone Polarity on Aggregation and Conduction of Ions in Polymer Electrolytes

Abstract

The usual understanding in polymer electrolyte design is that increasing the polymer dielectric constant results in reduced ion aggregation and therefore increased ionic conductivity. We demonstrate here that in a class of polymers with extensive metal-ligand coordination and tunable dielectric properties, the extent of ionic aggregation is delinked from the ionic conductivity. The polymer systems considered here comprise ether, butadiene, and siloxane backbones with grafted imidazole side-chains, with dissolved Li + , Cu 2+ , or Zn 2+ salts. The nature of ion aggregation is probed using a combination of X-ray scattering, electron paramagnetic resonance (in the case where the metal cation is Cu 2+ ), and polymer field theorybased simulations. Polymers with less polar backbones (butadiene, and siloxane) show stronger ion aggregation in X-ray scattering compared to those with the more polar ether backbone. The Tg-normalized ionic conductivities were however unaffected by extent of aggregation. The results are explained on the basis of simulations which indicate that polymer backbone polarizability does impact the microstructure and the extent of ion aggregation, but does not impact percolation, leading to similar ionic conductivity regardless of the extent of ion aggregation. The results emphasize the ability to design for low polymer Tg through backbone modulation, separately from controlling ion-polymer interaction dynamics through ligand choice.

Structure Code for Advanced Polymer Electrolyte in Lithium‐Ion Batteries

“…[ 31,194 ] Although the polymer matrices with different structures have already taken a place in the preparation of excellent electrolyte materials for LIBs, [ 32 ] current studies on the relationship of polymer structure and electrolyte property are neither pervasive nor systemic, and it is yet to be reviewed. [ 32b,33 ] Herein, we present a series of PEs developed based on well‐defined polymer hosts, and analyze the effect of the polymer structures on ionic conductivity, mechanical properties, processability, accessibility, and other properties ( Figure ). Moreover, specific functions of the developed PE materials attributed to their targeted structural design, such as self‐healing, flame‐retardance, are discussed.…”

Rational design of charge-functional materials: Insights from molecular engineering and operando imaging

“…Elucidation of ionic-transport phenomena has remained a challenging task since ions could be represented by various types of species (e.g., multivalent ions, large ion clusters, and ions with amphiphilic structure). 20,21 In certain types of materials (e.g., conjugated polymer films and graphitized carbon fibers), both electronic and ionic transport can occur, and can be strongly coupled under certain operation conditions (e.g., charging in an electrolyte solution). 17,[22][23][24] Importantly, the degree of coupling usually determines the properties and performance of related devices such as organic electrochemical transistors 22 and solid-state lithium-metal batteries.…”

Glass Transition Temperature and Ion Binding Determine Conductivity and Lithium–Ion Transport in Polymer Electrolytes

“…Metal-ligand coordination polymers enable tunable dynamic interactions between cations and ligands tethered to a polymer backbone [12][13][14][15] and promote salt dissolution even with low polarity polymer backbones, 16 providing a large library of polymers for optimizing conductivity performance. 10,16,17 Ion conduction in polymer electrolytes is achieved through the dissolution of a metallic salt and subsequent transport of the metal cation and organic anion. [18][19][20] Polymer electrolytes must therefore contain solvating groups that interact with ions (typically the cation) to stabilize ionic species but still allow for ion mobility.…”

“…We have previously demonstrated the dynamic metal-ligand coordination of imidazole-containing polymers towards lithium and other metal ions, suggesting this class of materials satisfies these requirements. 10,16,17 Figure 1. Structure comparison between the amide-free (PMS-10-Im) and the amide-containing (PMS-6-Amide-3-Im) polymers.…”

“…The amide-free imidazole-grafted siloxane polymer (PMS-10-Im) was compared to the previously reported 16 amidecontaining version (PMS-6-Amide-3-Im) to identify whether the amide group enhanced or decreased Li + -ion transport. The two-step synthesis of PMS-6-Amide-3-Im polymer started with an addition reaction between γ-thiobutyrolactone and 1-(3-aminopropyl)imidazole to yield the corresponding thiol- containing product.…”