A basic element of lithium ion battery technology are Solid Polymer Electrolytes (SPEs). Specifically, progress on understanding the ion conduction mechanism in SPEs is anticipated to strongly affect the development of electromobility (all new cars will be hybrid or exclusively electrical, from 2030 onwards). In this Thesis, we study a series of novel SPEs, aiming at (a) unravelling the mechanism of ionic conduction and the factors that influence it, and (b) exploring the possibility of further increase. For this reason, novel SPEs based on: Discotic Liquid Crystals (DLCs), (b) block copolymers with complex macromolecular architectures and (c) Polymerized Ionic Liquids (PILs) were designed and investigated herein. In the first part of this study, the ionic conductivity and the mechanical stability of novel electrolytes based on discotic liquid crystals (DLC) of hexa-peri-hexabenzocoronenes (HBC) (also known as nanographenes), symmetrically substituted with six triethyleneglycol (TEG) chains and further doped with an electrolyte (LiCF3SO3), were studied. The columnar self-assembly of the HBC cores improves the mechanical stability of the system. Doping with LiCF3SO3 revealed that ions are exclusively incorporated in the TEG phase, leading to theformation of an ionic superstructure, that surrounds the HBC columns (with a helical conformation). Τhe ionic superstrucure further improves the mechanical stability of the system (. Subsequently, it was shown that the asymmetric substitution of the HBC cores with two PEG chains, destabilize the ionic superstructure and increase the room temperature ionic conductivity by two decades (from toIn the second part, we studied the effect of macromolecular architecture (in a series of novel block copolymers based on electrtolytes) on ionic conductivity. More specifically, electrolytes based on “densely grafted” poly(ethylene oxide) (PEO) on a poly(hydroxylstyrene) (PHOS) backbone (PHOS-g-PEO), as well as diblock copolymers with polystyrene (PS) (PS-b-(PHOS-g-PEO)) were synthesized. The diblock copolymer combines the conductive phase of PEO/electrolyte with the mechanical stability of glassy PS. It was demonstrated that this specific macromolecular design, reduces or even suppresses the crystallinity of both PEO and the complex crystals, thus increasing ionic conductivity. Typically, at 303 K and at 373 K, the ionic conductivity for the block-grafted system with salt concentration [ΕΟ]:[Li+] = 12:1 was ∼3 × 10−7 S·cm-1 and ~ 3× 10−4 S·cm-1, respectively. Atthe same time, the densely grafted electrolytes show improved mechanical stability, that is required for applications as SPEs. In the third part, we report the results of a combined work based on density functional theory (DFT) calculations and experiments of the factors that influence the glass temperature, Tg, and the associated ion conductivity in polymerized ionic liquids bearing imidazolium salts in the side group. This study consists of four different N-alkyl side-chain lengths [with n = 4 (butyl), 6 (hexyl), 8 (octyl), and 10 (decyl)] and seven different counteranions ([Br]-, [BF4]-,[ClO4]-, [PF6]-, [Picrate]-, [TFSI]-, and [B(Ph)4]-). DFT calculations of the anion−cationcomplexation energies were combined with thermodynamics (differential scanning calorimetry), structural (X-ray scattering), as well as temperature- and pressure-dependent dielectric spectroscopy measurements of ion conduction. Our results show that ion conduction is facilitated by local anion jumps with a length scale on the order of the charge alteration distance. Ion complexation strongly influences the backbone dynamics and the associated Tg. A simple “stick and jump” model can account for the increased backbone mobility (reduced Tg) and the concomitant enhanced ion conductivity for anions with intermediate size. Among the different anions, [TFSI]− with its comparably large size and broad charge delocalization is only weakly coordinated with the cation. This best facilitates anion motion within the “ion paths” of the hexagonally packed cylinders and smectic morphologies. The results above may help in the design of new SPes with application in future lithium-ion batteries. In addition, the last two systems, based on the DLCs of nanographenesand the PILs with the polythiophene backbone provide with more possibilities: they can support simultaneous ionic and electronic conduction from the PEG and graphene/polythiophene respective “channels” at the nanoscale (e.g. ionic/semiconductors).
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