The synthesis of a new family of boron-based anion receptors and the study of their effect on ion pair dissociation and conductivity of lithium salts in nonaqueous solutions

Article abstract of DOI:10.1149/1.1838719

A new family of anion receptors based on boron compounds has been synthesized. These compounds can be used as anion receptors in lithium battery electrolytes. This family includes various borane and borate compounds with different fluorinated aryl and fluorinated alkyl groups. When these anion receptors are used as additives in 1,2-dimethoxyethane (DME) solutions containing various lithium salts, the ionic conductivities of these solutions are greatly increased. The electrolytes tested in this study were DME solutions containing the following lithium salts: LiF, LiCl, LiBr, LiI, CF₃COOLi, and C₂F₅COOLi. Without the additive, the solubility of LiF in DME (and all other nonaqueous solvents) is very low. With some of these boron compounds as additives, LiF solutions in DME with concentration as high as 1 M were obtained. The solubilities of the other salts were also increased by these additives. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy studies show that Cl^- and I^- anions are complexed with these compounds in DME solutions containing LiCl or LiI salts. The degree of complexation is also closely related to the structures of the fluorinated aryl and alkyl groups, which act as electron-withdrawing groups. The NEXAFS results are in good agreement with ionic conductivity studies.