Chapter 9 - Electrochemical properties of lithium electrolytes based on bis(polyfluorodiolato)borate and tetrakis(polyfluoroalkoxy) aluminate superweak anions

Abstract

This chapter provides information on the electrochemical properties of lithium electrolytes based on bis (polyfluorodiolato) borate and tetrakis (polyfluoroalkoxy) aluminate superweak anions. Many lithium salts of molecular anions have been considered as potential ionic components of electrolytes for primary and secondary lithium-ion batteries. Simple salts such as LiClO4, LiBF4, LiPF6, LiAsF6, and LiCF3SO3 fail to meet one or more of the accepted performance criteria. A growing class of new lithium salts contains a variety of new borate anions that contain two or more fluorine atoms. This improves the electrochemical stability and generally increases the conductivity at a given salt concentration. The chapter reviews work on the electrochemical properties of nine electrolyte salts based on the formula LiB(OC(2-OC6H4_nFn)(CF3)2)2 (n _ 0–3) [5] and, for comparison, the six related electrolyte salts LiAl(OCR(CF3)2)4 (R _ H, Me, CF3, Ph), LiAl(OCH2CF3)4, and LiAlF(OCPh(CF3)2)3. It aims to arrive at a practical replacement for LiPF6 in lithium batteries. It also emphasizes the understanding of the steric and electronic factors.