Solid-state polymer electrolytes have received substantial attention in the effort to revive high-energy-density Li-based batteries. In order to increase the capacity of Li-based batteries, researchers have largely focused on new electrode materials: regarding cathodes, Li–air and Li–sulfur batteries represent leading frontier candidates while at anode, Li-metal can replace graphite to increase anode energy density by approximately tenfold. Anyway, electrode advancements require an enabling electrolyte to combat irreversible reactions and dendrite growth during long-term charge/discharge cycling. In order to avoid these issues, solid-state polymer electrolytes should not only provide mechanical stiffness to block dendrites, but also should deliver safer (thermal stability without the leakage, flammability or volatility) operation compared to liquid electrolytes. Ionic liquid gel polymer electrolytes, made by immobilizing Li-salts dissolved in ionic liquids in a polymer matrix or polymerized ionic liquids have received increasing attention due to their potential applications in electrochemical devices. However, because of the trade-off between mechanical properties and ionic conductivity, the preparation of ionic liquid gel polymer electrolytes with both high ionic conductivity and robust mechanical properties remains challenging. In order to achieve high ionic conductivities in these systems, researchers have concentrated in synthesis polymerized ionic liquids with lower glass transition temperatures; unfortunately the higher ionic conductivity was achieved in detriment of mechanical properties. We have recently developed a class of solid electrolytes, termed polymeric ionic composites (PIC), composed of Li-salt dissolved in ionic liquids (IL) and a rigid-rod polyelectrolyte, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT). PIC materials, obtained through an ion-exchange process between IL and PBDT aqueous solution, possess an unprecedented combination of high ionic conductivity (>3 S/cm @RT), high thermal stability, low flammability, and widely tunable tensile storage moduli. This PIC material fabrication platform shows promise for safe and high-energy-density energy storage and conversion applications, incorporating the fast transport of ceramic-like conductors with the superior flexibility of polymer.

Acknowledgements: This work was supported by the grants of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-TE-2019-1734, within PNCDI III, PN 19110204 and by a grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI – UEFISCDI, project number ERANET-M-SMICE-Li, within PNCDI III”.

References:

1. C. Iacob, A. Matsumoto, H. Liu, S. Paddison, J. Sangoro, O. Urakawa, T. Inoue and J. Runt. Polymerized Ionic Liquids: Correlation of Ionic Conductivity with Nanoscale Morphology. ACS Macro Letters, 2017, 6, 9, 941-946.

2. C. Iacob and J. Runt, Charge transport of polyester ether ionomers in unidirectional silica nanopores, ACS Macro Letters, 2016, 5, 476-480.

3. Atsushi Matsumoto, Francesco Del Giudice, Rachapun Rotrattanadumrong, and Amy Q. Shen, Rheological Scaling of Ionic-Liquid-Based Polyelectrolytes in Ionic Liquid Solutions, Macromolecules, 2019, 52, 2759-2771.

3. J.E Bostwick, CJ Zanelotti, C Iacob, AG Korovich, LA Madsen, RH Colby, Ion transport and mechanical properties of non-crystallizable molecular ionic composite electrolytes, Macromolecules, 2020, 53 (4), 1405-1414.