Michal Jan Kalita

Fluorine-free electrolytes for all-solid sodium-ion batteries based on percyano-substituted organic salts

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.

Anion-Additive Interactions Studied by Ab Initio Calculations and Raman Spectroscopy

The ability of the caLi x (6)pyrrole (C6P) additive to form complexes with several anions is addressed. Ab initio calculations and Raman spectroscopy are used in combination to evaluate the coordination preferences of C6P in the gas phase and to probe the existence of C6P-anion complexes in solution. Favorable reaction energies are calculated for the formation of 1:1 coordination complexes from the isolated species, with the following anion preference: BF 4 - AsF 6 - > ClO 4 - ≈CF 3 SO 3 - > PF 6 - > I - . In connection with available macroscopic data, the calculated results support the assumption of anion coordination by C6P as a mechanism for lithium transference number enhancement. Upon anion coordination to the additive, calculated vibrational spectra show large differences in the N-H stretching region (∼3400 cm -1 ). However, at lower wavenumbers ( < 3300 cm -1 ) no significant differences are predicted. The latter is in agreement with experimental Raman data for the three examined samples: C6P, C6P-AsF 6 -, and C6P- I - .