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

Abstract

Lithium hexafluorophosphate (LiPF 6 ) is the best electrolyte for lithium-ion batteries because of its excellent performance. The conversion of KPF 6 into LiPF 6 is a green chemical process. However, KPF 6 residues are introduced into the electrolyte during the preparation process. In this study, we evaluated the effects of KPF 6 on the electrochemical performance of natural graphite/Li. The results of a cycling test showed that as the KPF 6 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 KPF 6 . Cyclic voltammograms showed that the addition of KPF 6 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% KPF 6 did not change the main components of the SEI film, but the ROCO 2 Li content decreased and the Li 2 CO 3 content increased. Therefore, the electrochemical performance of the graphite electrode was improved by lithiumion migration on the SEI film, which protected the graphite layer.

Could K+‐Based Electrolytes Be the Reliable Environmental‐Friendly Alternative to Li+ in Gr//LMO Battery We Searched for?

“…[ 49 ] This hypothesis is supported by Zheng et al and Xia and et al who reported that potassium increases the conductivity of graphite when used in limited amounts [ 50 ] and makes Li migration through SEI easier. [ 51 ] Naveen et al recently demonstrated [ 52 ] that during the first charge of O 3 –NaCrO 2 in K + ‐containing electrolytes, Na 0.52 CrO 2 can reversibly accommodate K + with no interference with Na + . They revealed by density functional theory (DFT) computation that the rearrangement of Na + is an energetically favored process rather than a homogeneous distribution of Na + /K + , which explains why repeated K + insertion/deinsertion in a Na‐based cathode contributes to superior electrochemical properties at fast C rates.…”

Controlling Li Dendritic Growth in Graphite Anodes by Potassium Electrolyte Additives for Li-Ion Batteries

“…28,29 In addition, K + improved the electrochemical performance by expanding the graphite layers (due to larger K + intercalation) in the very first charge and increasing the Li 2 CO 3 SEI compound respectively, which reportedly favored the Li + intercalation. 30,31 Furthermore, enhanced Li + kinetics was confirmed with a K 2 CO 3 coating on graphite anodes, compared to the Na equivalent. 32 However, Komaba et al observed the inferior electrochemical behavior of potassium electrolyte additives compared with Na + .…”

“…The increased inorganic components in SEI enhances its mechanical strength and Li + ion diffusion, thereby reinforcing its stability against dendritic growth . Similarly, Zhuang and Zheng et al investigated various potassium salt additives, which were found to reduce the irreversible Li loss due to K accumulation in the double layer. , In addition, K + improved the electrochemical performance by expanding the graphite layers (due to larger K + intercalation) in the very first charge and increasing the Li 2 CO 3 SEI compound respectively, which reportedly favored the Li + intercalation. , Furthermore, enhanced Li + kinetics was confirmed with a K 2 CO 3 coating on graphite anodes, compared to the Na equivalent . However, Komaba et al observed the inferior electrochemical behavior of potassium electrolyte additives compared with Na + .…”