B07 • Perfluoroalkylboron Compounds for Battery Applications
Ion-conducting materials that function as electrolytes are essential in modern electrochemical devices. Borate anions have attracted particular attention due to the interesting properties that they endow on electrolytes, especially in battery applications. However, the number of different borates that have been studied in significant detail, either as conductive salts or as electrolyte additives, are limited to salts with only a few anions, e.g. [BF4]–, the difluoro(oxalato)borate (DFOB) anion and the bis(oxalato)-borate anion (BOB). Perfluoroalkylborates have received little attention for battery applications, which is surprising considering their typically high thermal, chemical, and electrochemical stability.
This project aims to (I) develop efficient syntheses of new perfluoroalkylborates and (II) investigate the properties of medium-to-weakly-coordinating perfluoroalkylborate anions as component of conductive salts, either as metal salts or ionic liquids (ILs). In particular, compounds which can function as electrolyte additives are interesting as they have the potential to significantly influence the battery performance. In this regard, not only the lithium salts, but also related neutral boron-containing compounds, will be investigated as additives. The synthetic focus (M. Finze) will be on borate anions with two or more perfluoroalkyl groups including tetrakis(perfluoroalkyl)borate anions [BRF4]– since a higher number of perfluoroalkyl groups usually leads to an increase in stability. As additives, particularly for film-forming additives, where decomposition under specific conditions is desired, related neutral compounds or partially fluorinated derivates will also be explored. The electrolyte studies (G. Giffin) will focus on formulations involving the use of additives or novel salts for lithium-ion batteries (LIBs) and their testing in the device fabrication with promising candidates during the first funding period. The lessons learned can be extended to other active metal cations (e.g. other M+ or M2+ cations) in the second funding period.
