Achieving Fast and Efficient K⁺ Intercalation on Ultrathin Graphene Electrodes Modified by a Li⁺ Based Solid-Electrolyte Interphase

Advancing beyond Li-ion batteries requires translating the beneficial characteristics of Li⁺ electrodes to attractive, yet incipient, candidates such as those based on K⁺ intercalation. Here, we use ultrathin few-layer graphene (FLG) electrodes as a model interface to show a dramatic enhancement of K⁺ intercalation performance through a simple conditioning of the solid-electrolyte interphase (SEI) in a Li⁺ containing electrolyte. Unlike the substantial plating occurring in K⁺ containing electrolytes, we found that a Li⁺ based SEI enabled efficient K⁺ intercalation with discrete staging-type phase transitions observed via cyclic voltammetry at scan rates up to 100 mVs^-1 and confirmed as ion-intercalation processes through in situ Raman spectroscopy. The resulting interface yielded fast charge-discharge rates up to ∼360C (1C is fully discharge in 1 h) and remarkable long-term cycling stability at 10C for 1000 cycles. This SEI promoted the transport of K⁺ as verified via mass spectrometric depth profiling. This work introduces a convenient strategy for improving the performance of ion intercalation electrodes toward a practical K-ion battery and FLG electrodes as a powerful analytical platform for evaluating fundamental aspects of ion intercalation.