Coordination Abilities of 4,5-Dicyano-2-(trifluoromethyl)imidazolate Anion toward Sodium Cation: Structural and Spectroscopic Studies of Solid and Liquid Glyme-Solvated Electrolyte Systems

Comprehensive structural analysis of sodium 4,5-dicyano-2-(trifluoromethyl)­imidazolate (NaTDI) solvates with glymes (1–4), tetrahydrofuran, and crown ethers has been performed. Several structural motifs obtained from single-crystal X-ray analysis of complementary series of crystalline adducts with varying O:Na ratios were correlated with spectroscopic and thermal data to provide new information about the coordination ability of heterocyclic anions toward sodium cations. Presented results provide a basis for developing models of poly­(ethylene oxide) electrolytes and liquid systems for sodium ion battery electrolytes. We have found a wide variety of anion–cation coordination types which allow us to compare them with analogous lithium solvates in terms of Brown’s valence-matching principle and Lewis acid strength (<i>S</i>_a) parameters. Noticed aggregation modes of sodium salts confirm the occurrence of a solvate disproportionation conductivity mechanism at high salt concentrations which can be used for developing new heterocyclic salt systems for sodium batteries

New Tailored Sodium Salts for Battery Applications

This article describes synthesis and basic electrochemical and structural properties of newly designed sodium salts for application in liquid nonaqueous sodium electrolytes. There has been two imidazole fluorine derivative sodium salts synthesized: sodium 4,5-dicyano-2-(trifluoromethyl)­imidazolate (NaTDI) and sodium 4,5-dicyano-2-(pentafluoroethyl)­imidazolate (NaPDI). The structure of the salts has been confirmed by means of Raman spectroscopy, nuclear magnetic resonance (¹³C NMR and ¹⁹F NMR), X-ray diffraction, thermogravimetry (TGA), and differential scanning calorimetry (DSC). Electrochemical characterization included ionic conductivity measurements, dynamic viscosity, and electrochemical stability of solutions of the salts in propylene carbonate (PC) at different temperatures. Raman spectra of the electrolytes have been performed to carefully monitor the degree of ionic associations specially ion pairing tendencies