Improved synthesis of a highly fluorinated boronic ester as dual functional additive for lithium-ion batteries

The electrolyte additive 2-(pentafluorophenyl)-tetrafluoro-1,3,2-benzodioxaborole (PFPTFBB, 1) was found to have a reversible redox potential at 4.43 V vs. Li+/Li. This compound can function as an overcharge protection additive as well as anion receptor for lithium-ion batteries. It has drawn a great deal of interest from industry, but its use in relatively large quantities is limited by the production challenges of tetrafluorocatechol (TFC, 3), which is the key starting chemical for the synthesis of PFPTFBB. As part of a continuous effort in our research toward improving the safety of lithium-ion batteries, we have performed the synthesis of TFC and optimized its synthesis process. The X-ray single-crystal structures of TFC and the intermediate product 5,6,7,8-tetrafluoro-1,4-benzodioxane (4) during the process of PFPTFBB synthesis are reported for the first time. Also presented is the lithium ion cell performance of PFPTFBB as redox shuttle in various electrolyte systems.