The complex interplay between the ionic conductivity and structure of the LiCF 3 SO 3 :PEO polymer electrolyte, induced by the calix͓6͔pyrrole anion receptor, has been investigated by different experimental methods, including ac impedance, calorimetry, X-ray diffraction, and Fourier-transform infrared spectroscopy. It was found that calix͓6͔pyrrole, even at low concentrations, can form stable bidentate complexes with triflate anions, thus making cation transport dominating, which results in t + close to unity. It should be noted that the incorporation of an anion trap does not suppress the bulk ionic conductivity of polymer electrolytes at above 60°C. We attribute this effect to the dissociation of ion aggregates and structural changes imposed by the additive. Stable solid electrolyte interface resistance was achieved in the polymer electrolytes containing calix͓6͔pyrrole.
A new family of fluorine-free solid-polymer electrolytes, for use in sodium-ion battery applications, is presented. Three novel sodium salts withdiffuse negative charges: sodium pentacyanopropenide (NaPCPI), sodium 2,3,4,5-tetracyanopirolate (NaTCP) and sodium 2,4,5-tricyanoimidazolate (NaTIM) were designed andtested in a poly(ethylene oxide) (PEO) matrix as polymer electrolytes for anall-solid sodium-ion battery. Due to unique, non-covalent structural configurations of anions, improved ionic conductivities were observed. As an example, “liquid-like” high conductivities (>1 mS cm−1) were obtained above 70 °C for solid-polymer electrolyte with a PEO to NaTCP molar ratio of 16:1. All presented salts showed high thermal stability and suitable windows of electrochemical stability between 3 and 5 V. These new anions open a new class of compounds with non-covalent structure for electrolytes system applications.
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