Decoupling Interfacial Kinetics Realizes 5C Fast Charging of Potassium‐Ion Batteries Using Graphite Anode

Abstract Improving interfacial kinetics is the key to realizing extreme fast charging (XFC) of graphite‐based potassium ion batteries (PIBs). The electrolyte engineering is commonly used for solid electrolyte interphase (SEI) design. However, this strategy adjusts both ion solvation structure and (de)solvation kinetics simultaneously, thus making it difficult to explicitly reveal the linkage between SEI properties and interfacial kinetics. Herein, the content of inorganic species in preformed SEI on graphite surface is precisely regulated and uncovered its critical role in improving the interfacial kinetics. The charge transfer kinetics on graphite/electrolyte interphase is found to be the rate limitation step upon XFC. Meanwhile, the increased inorganic species in SEI plays a decisive role in optimizing the charge transfer rather than the kinetics of naked K + crossing SEI. Through unlocking the anodic charge transfer limitation with ultra‐inorganic rich SEI, the graphite//Prussian blue analogs full cells achieve a superior XFC ability (13 min charge to 80%) with a specific capacity of 103 mAh g −1 at 5 C. This work provides a fundamental understanding of the relationship between SEI properties and interfacial kinetics during XFC, which enables the rational design of SEI chemistry for fast‐charging PIBs.