Mechanistic Insights into the Intercalation and Interfacial Chemistry of Mesocarbon Microbeads Anode for Potassium Ion Batteries

Mesocarbon microbeads (MCMB) are highly desirable as anode materials for rechargeable potassium ion batteries (PIBs) due to their commercially availability, high stability and low-cost. However, their charge storage and interfacial mechanisms are still unclear. In this work, the intercalation mechanisms and the solid-electrolyte-interphase (SEI) formation of the MCMB in four different electrolytes is comprehensively studied. The MCMB anodes exhibit superior rate and cycle performances via a naked K-ions sequentially staging intercalation mechanism, realizing the complete transformation from graphite to KC8 . Whereas a solvated K-ions co-intercalation mechanism of the MCMB occurs in ether-based electrolytes, which might induce graphite exfoliation and result in unsatisfied specific capacity and capacity decay. Nevertheless, this co-intercalation behavior could be effectively suppressed by a highly concentrated electrolytes. Interfacial analyses unveil the distinct SEI components, which vary with the electrolyte chemistries. These SEI components also varies from surface to bulk and especially attention should be paid to the accurate control of the concentration of the fluoroethylene carbonate additives. This work provides a panoramic understanding of the intercalation and interfacial mechanisms on the MCMB anodes for PIBs.