Effect of KBF4 additive on high voltage cycling performance of lithium-ion batteries

Abstract Potassium tetrafluoroborate (KBF4), as a high-efficiency electrolyte additive, effectively enhances the electrochemical performance of LiCoO2/Li cells operating under high charging cut-off voltage. The KBF4 additive contributes towards the formation of a lower impedance and stable cathode electrolyte interface on the LiCoO2 cathode surface. This suppresses the subsequent oxidative decomposition of the base electrolyte, which allows the crystal structure of LiCoO2 to be maintained and transition metal leaching from LiCoO2 to be minimised, thus resulting in a significant improvement in the cycling and rate performance. Accordingly, cells with 0.5 wt% KBF4 electrolyte achieve an excellent capacity retention of 85.1% over 300 cycles over a voltage range of 3.0–4.5 V, whereas that of cells with the base electrolyte is only 64.7%. Moreover, KBF4, as a functional additive for high charging cut-off voltage, improves LiNi0.6Co0.2Mn0.2O2/Li cells. Cells with 1.0 wt% KBF4 and base electrolyte exhibit a superior capacity retention of 83.3% and 56.7%, respectively, over 200 cycles for voltage range 3.0–4.5 V.