Comparative Study of Alkali‐Cation‐Based (Li+, Na+, K+) Electrolytes in Acetonitrile and Alkylcarbonates

• Published in: Chemphyschem 2019-02, Vol.20 (4), p.581-594
• Main Authors: Amara, Samia, Toulc'Hoat, Joël, Timperman, Laure, Biller, Agnès, Galiano, Hervé, Marcel, Corinne, Ledigabel, Matthieu, Anouti, Mérièm
• Format: Article
• Language: English
• Subjects: Acetonitrile; Batteries; Cations; Chemical Sciences; Comparative studies; effective radius; Electrochemical analysis; Electrolytes; iconicity; ionic dissociation; Lithium; Mathematical analysis; polarizability; Sodium; Solvents; viscosity
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.201801064

The development of a suitable functional electrolyte is urgently required for fast‐charging and high‐voltage alkali‐ion (Li, Na, K) batteries as well as next‐generation hybrids supercapacitors. Many recent works focused on an optimal selection of electrolytes for alkali‐ion based systems and their electrochemical performance but the understanding of the fundamental aspect that explains their different behaviour is rare. Herein, we report a comparative study of transport properties for LiPF6, NaPF6, KPF6 in acetonitrile (AN) and a binary mixture of ethylene carbonate (EC), dimethyl carbonate (DMC): (EC/DMC : 1/1, weigh) through conductivities, densities and viscosities measurements in wide temperature domain. By application of the Stokes‐Einstein, Nernst‐Einstein, and Jones Dole equations, the effective ionic solvated radius of cation (reff), the ionic dissociation coefficient (αD) and structuring Jones Dole's parameters (A, B) for salt are calculated and discussed according to solvent or cation nature as a function of temperature. From the results, we demonstrate that better mobility of potassium can be explained by the nature of the ion‐ion and ion‐solvent interactions due to its polarizability. In the same time, the predominance of triple ions in the case of K+, is a disadvantage at high concentration. A comparative study of the transport properties of LiPF6, NaPF6, and KPF6 is performed in acetonitrile and alkylcarbonate to investigate the potential of these materials as energy‐storage electrolytes. The mobility of the alkali cations in the solvents is found to be dominated by their polarizability with the mobility of K+ being better in acetonitrile.