From polymer electrolytes to calcium-conducting ionomers: A route towards rechargeable calcium batteries?

Abstract

This work presents the synthesis of a new family of ionic monomers based on a diallylamine structure, designed to develop ionomers capable of conducting several types of monovalent and divalent cations (Li⁺, Na⁺, Ca²⁺, etc.). For this purpose, polymer electrolytes based on lithium and calcium salts at different O/M ratios are prepared using dialyzed poly(oxyethylene) (^DIAPOE) as polymer backbone. These polymer electrolytes are fully characterized in terms of microstructure (scanning electronic microscopy, X-Ray mapping), thermal properties (thermogravimetric analysis, differential scanning calorimetry) and ionic conductivity (electrochemical impedance spectroscopy) to elucidate the underlying ion diffusion mechanisms. To validate the reliability of the proposed ionomers and their synthesis procedure, a series of films were produced by crosslinking the corresponding ionic monomers, IMO_fr, with an unsaturated poly(oxyethylene), yielding IMO_fr-NPC1000 ionomers. The results show that ^DIAPOE membranes exhibit higher ionic conductivity at high temperatures, achieving values in the range of 10^–4 S cm^-1. To further promote ionic conductivity at ambient temperature, the cross-linked structure of IMO_fr-NPC1000 electrolytes were swelled in different polar solvents, demonstrating a conductivity increase of about two orders of magnitude without compromising their physical integrity. This study paves the way for the development of single-cation conducting ionomeric electrolytes towards safer, reliable and sustainable energy storage devices.