New trivalent imidazole-derived salt for lithium-ion cell electrolyte

Abstract

Lithium-ion cells utilize almost exclusively monovalent lithium salts as main electrolyte component. Apart from scarce works on sulfonyl imide derivatives, even in terms of basic parameters little is known about multivalent lithium salts' behavior in electrolytes. Here we present the new trivalent lithium salt dedicated to electrolytes for lithium-ion cells. Trilithium 2,2′,2″-tris(trifluoromethyl)benzotris(imidazolate) (Li3BTI) synthesis and its performance in PC and EC:DMC solutions is described in this paper. The structure and stability of this new lithium salt was fully characterized by NMR and Raman techniques as well as thermal methods. Basic electrochemical parameters of electrolytes based on this salt were done by linear sweep voltammetry, lithium cation transference number and conductivity measurements. The salt was designed specifically to manifest extraordinarily high lithium cation transference number (0.73 in EC:DMC 1:1 ratio mixture). However this new salt exhibits also thermal stability of 160 °C and electrochemical stability up to 4.5 V vs Li, as well as conductivities of the 1 mS cm−1 order of magnitude in liquid electrolytes. Promising compatibility results of the obtained electrolyte against Si/C composite anodes are also reported in this paper.