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Mono-Endcapped single-ion polymer electrolytes : Synthesis & Lithium-ion transport properties

Mercredi 27 mars 13:30 - Duree : 4 heures 30 minutes
Lieu : Amphithéâtre 2A003 au bâtiment GreEn-ER 21 Avenue des Martyrs - CS 90624 38031 GRENOBLE Cedex 1

Orateur : Soutenance de Thèse de Philip OVERTON (CEA-Liten/DEHT/STB/LM & UMR5819-SyMMES (CNRS/CEA/UGA)

Abstract : “Single Ion” Polymer Electrolytes (SIPEs) are foreseen as one of the solutions for enabling next generation solid-state electrolytes for Lithium-ion batteries.[1] Indeed, non-flammable viscoelastic polymers reduce the security risk of electrochemical cells associated with liquid electrolytes. Single Ion conductors, wh erein the fraction of ionic charge carried by lithium cations approaches unity, moreover avoid unfavourable side-reactions, the increase of interfacial resistance and the polarisation of the electrochemical cell caused by the unequal mobility of anionic vs. cationic species in formulations of binary salts. Building on the established performance of electrolytes based on poly(ethylene oxide), the presented "MonoEnd-Capped Single-Ion Polymer Electrolytes" (MEC-SIPEs) are ionically conductive polymers having n repeating ethylene oxide (EO) units and an ionic functional group at one chain terminal. The anions of the electrolyte salt pair are covalently bound to the polymer chain, affording single ion conductivity. The fraction of transferred Li+ indeed approaches unity (t+Li = 0.7-1.0). Using a simple and generic design, these MEC-SIPES achieve state-of-the-art ionic conductivity in the 20-100 °C temperature range : σAC> 0.1 mS/cm at T> 40°C and 1.0 mS/cm at 100°C. Characterisation of their electrochemical stabilities promotes these as candidates for cell chemistries operating in the 0-3.7 V vs. Li/Li+ range. The end-group designs target additionally other specific non-covalent interactions such as dipole-dipole, Van der Waals, and π-π stacking. End-groups having Polycyclic Aromatic H ydrocarbon (PAH) moieties are presented : a N-naphtyl sulfonamide (-SO2N(Li)Naphthalene), and secondary N-aryl amines (-N(Li)Naphthalene & -N(Li)Pyrene). Furthermore a "double salt" MEC-SIPE is presented, which has two ionic functions at one chain end, doubling the number of charge carriers per polymer chain. A zwitterionic MEC-SIPE, that conducts Li+ cations and TFSI- anions, has σAC> 0.1 mS/cm at T> 40°C (t+Li = 0.8 at 40°C) and retains ionic conductivity down to 0 °C. The performances of these new MEC-SIPEs surpass those having lithiated sulfonate end-groups (-SO3Li, -PhSO3Li), synthesized and characterised in this work in reference to the literature.[2]The performances of the MEC-SIPEs are benchmarked against Salt-in-Polymer (SiP) blends[3]of the state-of-the-art salt LiTFSI solvated by non-functionalised PEO having equivalent EO/Liratios. Against these standards, largely improved lithium transference numbers (t+Li) approaching unity and high ionic conductivities of MEC-SIPEs are highlighted. Finally, the ionic conductivity of MEC-SIPEs having 55 EO repeating units increase by 0.5 orders of magnitude under temperature cycling as revealed by electrochemical impedance spectroscopy. This phenomenon is first reported here and allows for the proposal of a tentative phenomenological ionic transport model for MEC-SIPEs based on detailed analyses of their thermal and ionic conductivity properties.

[1] Zhang et al., Chem. Soc. Rev. (2017), 46, 797.

[2] Ito et al., Solid State Ionics (1995), 79, 300. Ito et al., J. Mater. Chem. (1997), 7, 1357.

[3] Xue et al., J. Mater. Chem. A (2015), 3, 19218

Contact : patrice.rannou@cea.fr

Discipline évènement : (Biologie / Chimie)
Entité organisatrice : (LITEN)
Nature évènement : (Soutenance de thèse)
Site de l'évènement : Polygone scientifique

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