Effect of Substituting LiBF₄for LiPF₆in High Voltage Lithium-Ion Cells Containing Electrolyte Additives

This work evaluates the performance of LiBF 4 -containing electrolytes in lithium-ion cells charged to high voltages (>4.4 V) and explores the compatibility of LiBF 4 with additives known to improve the performance of LiPF 6 -based electrolytes. It was found that the benefit imparted by LiBF 4 is lost when cells are charged beyond 4.4 V, at which point electrolyte oxidation causes gas evolution and impedance growth. In the case of LiBF 4 , impedance growth is shown to be due to increased charge transfer resistance at the negative electrode, indicating poor passivation of the negative electrode. Of the additives tested, only those containing prop-1-ene-1,3-sultone benefit cells with LiBF 4 electrolyte at high voltage.