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 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.