Re-oxidation reconstruction process of solid electrolyte interphase layer derived from highly active anion for potassium-ion batteries

In our work, we obtain molybdenum sulfide-reduced graphene oxide (MS-RGO) composite and find that variation of anion in electrolyte could significantly affect the stability of MS-RGO composite for potassium-ion batteries (KIBs). Here, our MS-RGO composite presents a high capacity of 328 mAh g⁻¹ at 50 mA g⁻¹ after 50 cycles and a stable capacity of 170 mAh g⁻¹ after 500 cycles even at 1 A g⁻¹. We find that the anion of bisfluorosulfimide (FSI) in electrolyte can significantly improve the cycling stability compared with anion of hexafluorophosphate (PF). The excellent performance of battery in FSI-containing electrolyte should be attributed to the enhanced re-oxidation reconstruction process of solid electrolyte interphase (SEI) layer. The imperceptible re-oxidation reconstruction process of SEI layer under the effect of anion can be detected by differential capacitance analysis in each cycle. Meanwhile, we also confirm that the reaction activity of anion is a critical factor in determining the reconstruction process of SEI layer and the improvement of electrochemical performance. The enhanced re-oxidation reconstruction process derived from highly active anion not only complements existing knowledge on the failure mechanism of SEI layer, but also presents a new principle for electrolyte design to improve the performance of metal sulfides anodes for KIBs.