Elucidation of the Mechanism of K‐Ion Storage of Hard Carbon and Soft Carbon Anodes in Ether‐ and Ester‐Based Electrolytes

Abstract Graphite anodes experience co‐intercalation of K + ions and solvent in ether‐based electrolytes, which enables ultrafast kinetics of potassium‐ion storage. The potassium‐ion storage mechanisms of amorphous soft carbon (SC) and hard carbon (HC) anodes in ether‐based electrolytes are ambiguous. Herein, the co‐intercalation mechanisms of SC and HC in ether‐based electrolytes are elucidated. The solvated K + intercalates with a solvation structure, which avoids the sluggish desolvation process. Thus, HC and SC anodes display excellent rate capabilities. Moreover, the SC anode forms ternary K‐graphite intercalation compounds during the potassiation process. It is also demonstrated that solvated K + is not only stored in the spacing between graphene nanodomains but can also be stored in the closed pores of HC, enabling higher capacities than pure K + intercalation in ester‐based electrolytes. Nevertheless, the co‐intercalation causes the large volume expansion of SC and HC, giving rise to irreversible structural damage and capacity decay of SC and HC. The strong interaction between K + ions and ether molecules is the main reason for the co‐intercalation. A thick and organic‐rich solid electrolyte interphase film formed in ester‐based electrolytes can hinder the co‐intercalation in ether‐based electrolytes.