Ionic Conductivity in Polyfluorene-Based Diblock Copolymers Comprising Nanodomains of a Polymerized Ionic Liquid and a Solid Polymer Electrolyte Doped with LiTFSI

Abstract

Diblock copolymer electrolytes based on a π-conjugated polyfluorene (PF) backbone were synthesized comprising nanodomains of a polymerized ionic liquid (PIL) and of a solid polymer electrolyte (SPE). The former consists of a single-ion conductor based on an imidazolium alkyl chain with a [Br]− counteranion grafted on the PF backbone. The latter consists of short ethylene oxide (EO) chains, grafted on the PF backbone and further doped with LiTFSI. The two nanophases support ionic conductivity, whereas the rigid PF backbone provides the required mechanical stability. In the absence of LiTFSI, ionic conductivity in the PIL nanophase is low and exhibits an Arrhenius temperature dependence. LiTFSI substitution enhances ionic conductivity by about 3 orders of magnitude and further changes to a Vogel–Fulcher–Tammann temperature dependence. However, at ambient temperature, ionic conductivity is lower than in the corresponding PEO/LiTFSI electrolytes. X-ray studies and thermal analysis revealed that the conjugated backbone imparts liquid-crystalline order that can be fine-tuned through the EO side group length. Ionic conductivity measurements performed as a function of pressure identified local jumps of [Li]+ and [Br]− ions in the respective SPE/PIL nanophases as responsible for the ionic conductivity. Between the two ions, it is [Li]+ that has the major contribution to the ionic conductivity. The current results provide designing rules for new copolymers that comprise two different ionic nanodomains (PIL and SPE) and a conjugated backbone that can further support electronic conduction.

Side Chain Length-Dependent Dynamics and Conductivity in Self-Assembled Ion Channels

“…The real part of the complex conductivity of all ILCs studied here shows a frequency dependence similar to that of semiconducting disordered materials such as π conjugated ion conducting polymers, and ionic liquids Figure gives the frequency dependence of the real part of the complex conductivity for ILC14 and ILC16.…”

Recent Advances in Hole-Transporting Layers for Organic Solar Cells

“…CPEs composed of conjugated backbone and side chains containing ionic groups are attractive materials due to their intrinsic dual electronic and ionic conductivity, and good solubility in polar solvents [ 351 , 352 , 353 , 354 , 355 , 356 ]. Some examples of the chemical structure of CPEs used as HTLs are shown in Scheme 2 .…”

Ionic Conductivity of a Solid Polymer Electrolyte Confined in Nanopores

“…PEO is a promising polymeric matrix for such investigations. This is because of its high dielectric permittivity (to facilitate ion dissociation), its high solubility for Li salts, the high segmental mobility (low glass temperature), and nontoxicity. − On the other hand, LiTFSI is an excellent candidate for Li salt because the large molar volume (∼127 cm 3 ·mol –1 ) and low ion complexation energies promote Li-ion conductivity. The bulk properties of PEO/LiTFSI, including the ion conductivity in relation to the phase behavior have been widely investigated. − Little is known, however, about the extent to which the polymer chain dynamics and associated ionic transport are influenced by the nanoconfinement (e.g., in nanopores).…”

“…Both features could be explained by the adsorption of polymer segments in the framework of the scaling theory proposed by de Gennes. − The theory accounts for the formation of adsorbed layers by a highly cooperative process that involves several unfavorable chain configurations. Polymer adsorption affected the ion dynamics because ion transport is linked to the mobility of the polymer backbone. ,,,, This refers especiallybut not exclusivelyto the PEO backbone because of its ability to solvate salts through the interaction of cations with its ether oxygens. Overall, ion transport in confined space did not follow the bulk behavior as it was affected by polymer adsorption.…”