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Thomas F. Clément

Bottlebrush copolymers with ether and carbonate side-chains: From their macromolecular design to their use as electrolytes in lithium batteries

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Published on 26 March 2021
Thesis presented March 26, 2021

Abstract:
The energy density of current lithium metal batteries remain limited due to the reduced electrochemical stability at high potential of PEO-based electrolytes. Other families of polymer electrolytes have been investigated to overcome this issue, showing stability up to 5V vs Li+/Li. Polycarbonates are among these materials. In this context, this thesis describes the synthesis and development of poly(trimethylenecarbonate) (PTMC) based polymers and bottlebrush copolymers for their use as polymeric host matrices for lithium salts to allow for salt-in-polymer solid polymer electrolytes. We report the synthesis of PTMC by organocatalysed ROP of TMC, allowing the generation of an extended range of molecular masses combined with low dispersity (0.7kg.mol-1 < Mn < 50kg.mol-1 ; DPn < 1.18). The electrochemical characterizations of PTMC/lithium salts electrolytes are presented and discussed, allowing the optimization of these electrolytes (nature of the salt, concentration, Mn, etc.) and the tentative proposition of an ionic transport mechanism within these PTMC matrices. The syntheses of bottlebrush copolymers, based on a poly(pentafluorostyrene) (PPFS) backbone and PEO and PTMC side-chains (PPFS-g-PEO and PPFS-g-PTMC), allow to overcome low Young modulus values while keeping a high side-chain dynamics favorable to ion transport. At equivalent PTMC chain lengths (and Mn > 1.9kg.mol-1), PPFS-g-PTMC/LiTFSI has an ionic conductivity similar to that of their homopolymer electrolytes counterparts. Furthermore, comparison of bottlebrush copolymer electrolytes based on similar DPn PEO and PTMC side-chains show identical conductivity for T > 60°C. These studies are therefore a proof of concept for the use of these polycarbonate-based materials as polymer electrolytes for lithium metal batteries.

Keywords:
Macromolecular Chemistry: Organocatalyzed ROP and Ziegler-Natta polymerization
Macromolecular Engineering: Oligo/Polymer & Bottlebrush Copolymer, Polymer electrolyte,Ionic conductivity, Lithium Battery

On-line thesis.