Unravelling the mechanism of potassium-ion storage into graphite through electrolyte engineering

Graphite is one of the most widely used anode materials in potassium-ion batteries (PIBs). However, the exact mechanism of K+ions intercalation into graphite has not yet been fully understood. In addition, the intercalation process strongly depends on the selection of the electrolyte system. In this work, we evaluated the use of an electrolyte containing 1.5 M potassium bis(fluorosulfonyl)imide (KFSI) dissolved in a mixture of propylene carbonate (PC)/ 1,1,2,2-tetraethoxyethane (TEG)/ vinyl ethylene carbonate (VEC) (62:36:2 vol.%). Using such an electrolyte system it was possible to obtain experimental evidence for the formation of KC16 during the potassium intercalation and deintercalation using in situ Raman spectroscopy and operando X-ray diffraction (XRD). The results are supported by the visual observation of a color change of the graphite electrode surface during the intercalation of K+ ions into the graphite lattice. In addition, it has been demonstrated that the selected electrolyte system eliminates the co-intercalation of the solvent into the graphite structure.