Effects of KPF6 on the electrochemical performance of natural graphite/Li

Lithium hexafluorophosphate (LiPF6) is the best electrolyte for lithium-ion batteries because of its excellent performance. The conversion of KPF6 into LiPF6 is a green chemical process. However, KPF6 residues are introduced into the electrolyte during the preparation process. In this study, we evaluated the effects of KPF6 on the electrochemical performance of natural graphite/Li. The results of a cycling test showed that as the KPF6 content increased in the electrolyte, the specific capacity of the graphite electrode also increased gradually. The impedance of a solid electrolyte interphase (SEI) film was decreased by the addition of KPF6. Cyclic voltammograms showed that the addition of KPF6 had no effects on the insertion and extraction reactions of lithium ions on the graphite electrode. Analyses of the graphite electrodes using scanning electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy suggested that the addition of 0.09 and 0.2 wt% KPF6 did not change the main components of the SEI film, but the ROCO2Li content decreased and the Li2CO3 content increased. Therefore, the electrochemical performance of the graphite electrode was improved by lithium-ion migration on the SEI film, which protected the graphite layer.