Improving interfacial kinetics is the key to realizing extreme fast charging(XFC) of graphite-based potassium ion batteries (PIBs). The electrolyteengineering is commonly used for solid electrolyte interphase (SEI) design.However, this strategy adjusts both ion solvation structure and (de)solvationkinetics simultaneously, thus making it difficult to explicitly reveal the linkagebetween SEI properties and interfacial kinetics. Herein, the content ofinorganic species in preformed SEI on graphite surface is precisely regulatedand uncovered its critical role in improving the interfacial kinetics. The chargetransfer kinetics on graphite/electrolyte interphase is found to be the ratelimitation step upon XFC. Meanwhile, the increased inorganic species in SEIplays a decisive role in optimizing the charge transfer rather than the kineticsof naked K+ crossing SEI. Through unlocking the anodic charge transferlimitation with ultra-inorganic rich SEI, the graphite//Prussian blue analogsfull cells achieve a superior XFC ability (13 min charge to 80%) with a specificcapacity of 103 mAh g−1 at 5 C. This work provides a fundamentalunderstanding of the relationship between SEI properties and interfacialkinetics during XFC, which enables the rational design of SEI chemistry forfast-charging PIBs.