Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2024

ACL
doi

F.Makhlooghiazad, L.M.Guerrero Mejía, G.Rollo-Walker, D.Kourati, F.Chen, M.Galceran, M.Deschamps, P.Howlett, L.A.O’Dell, M.Forsyth, 'Understanding polymerized ionic liquids as solid polymer electrolytes for sodium batteries', J. Am. Chem. Soc. 146(3) 1992–2004 (2024) doi:10.1021/jacs.3c10510

Solid polymer electrolytes (SPEs) have emerged as promising candidates for sodium-based batteries due to their cost-effectiveness, and excellent flexibility. However, achieving high ionic conductivity and desirable mechanical properties in SPEs remains a challenge. In this study, we investigated an AB diblock copolymer, PS-PEA(BuImTFSI), as a potential SPE for sodium batteries. We explored binary and ternary electrolyte systems by combining the polymer with salt and [C3mpyr][FSI] ionic liquid (IL) and subjecting them to thermal and electrochemical analyses. Differential scanning calorimetry revealed phase separation in the polymer systems. The addition of salt exhibited a plasticizing effect localized to the poly-ionic liquid (PIL) phase, resulting in increased ionic conductivity in the binary electrolytes. Introducing the IL further enhanced the plasticizing effect, elevating ionic conductivity in the ternary system. Spectroscopic analysis, for the first time, revealed that the incorporation of NaFSI and IL influences the conformation of TFSI- and weakens the interaction between TFSI- and the polymer. This, in turn, establishes correlations between anions and Na+, ultimately enhancing the diffusivity of Na ions. The electrochemical properties of an optimized SPE in Na/Na symmetrical cells were investigated, showcasing stable Na plating/stripping at high current densities up to 0.7 mA.cm−2, maintaining its integrity at 70 °C. Furthermore, we evaluated the performance of a Na|NaFePO4 cell cycled at different rates (C/10 and C/5) and temperatures (50 °C and 70 °C), revealing remarkable high-capacity retention and coulombic efficiency. This study highlights the potential of solvent-free diblock copolymer electrolytes for high-performance sodium-based energy storage systems, contributing to advanced electrolyte materials.