Interlayer environment engineered MXene: Pre-intercalated Zn2+ ions as intercalants renders the modulated Li storage

The intercalation of foreign species into MXene, as an approach of tuning the interlayer environment, is employed to improve electrochemical ion storage behaviors. Herein, to understand the effect of confined ions by the MXene layers on the performance of electrochemical energy storage, Zn2+ ions were employed to intercalate into MXene via an electrochemical technique. Zn2+ ions induced a shrink of the adjacent MXene layers. Meaningfully, a higher capacity of lithium ion storage was obtained after Zn2+ pre-intercalation. In order to explore the roles of the intercalated Zn2+ ions, the structural evolution, and the electronic migration among Zn, Ti and the surface termination were investigated to trace the origination of the higher Li+ storage capacity. The pre-intercalated Zn2+ ions lost electrons, meanwhile Ti of MXene obtained electrons. Moreover, a low-F surface functional groups was achieved. Contrary to the first shrink, after 200 cycles, a larger interlayer distance was monitored, this can accelerate the ion transport and offer a larger expansile space for lithium storage. This may offer a guidance to understand the roles of the confined ion by two-dimensional (2D) layered materials.