Expanded interlayer spacing and additionally exposed edges induced by defects of MoS2 enable facile K-intercalation, rapid K-transport and promoted K-adsorption.

Unexpected intercalation-dominated process is observed during K + insertion in WS 2 in a voltage range of 0.01-3.0 V. This is different from the previously reported two-dimensional (2D) transition metal dichalcogenides that undergo a conversion reaction in a low voltage range when used as anodes in potassium-ion batteries. Charge/discharge processes in the K and Na cells are studied in parallel to demonstrate the different ion storage mechanisms. The Na + storage proceeds through intercalation and conversion reactions while the K + storage is governed by an intercalation reaction. Owing to the reversible K + intercalation in the van der Waals gaps, the WS 2 anode exhibits a low decay rate of 0.07% per cycle, delivering a capacity of 103 mAh•g −1 after 100 cycles at 100 mA•g −1. It maintains 57% capacity at 800 mA•g −1 and shows stable cyclability up to 400 cycles at 500 mA•g −1. Kinetics study proves the facilitation of K + transport is derived from the intercalation-dominated mechanism. Furthermore, the mechanism is verified by the density functional theory (DFT) calculations, showing that the progressive expansion of the interlayer space can account for the observed results.

Articles you may be interested inStructural and dielectric properties of laser ablated BaTiO3 films deposited over electrophoretically dispersed CoFe2O4 grains Raman spectroscopic study of Na1/2Bi1/2TiO3-x%BaTiO3 single crystals as a function of temperature and compositionThe low Curie temperature (T c ¼ 130 C) of bulk BaTiO 3 greatly limits its applications. In this work, the phase structures of BaTiO 3 nanoparticles with sizes ranging from 2.5 nm to 10 nm were studied at various temperatures by using aberration-corrected transmission electron microscopy (TEM) equipped with an in-situ heating holder. The results implied that each BaTiO 3 nanoparticle was composed of different phases, and the ferroelectric ones were observed in the shells due to the complicated surface structure. The ferroelectric phases in BaTiO 3 nanoparticles remained at 600 C, suggesting a significant increase of T c . Based on the in-situ TEM results and the data reported by others, temperature-size phase diagrams for BaTiO 3 particles and ceramics were proposed, showing that the phase transition became diffused and the T c obviously increased with decreasing size. The present work sheds light on the design and fabrication of advanced devices for high temperature applications.

Hierarchical Sb as an additive-free anode was fabricated to show excellent electrochemical performance for both Na-ion half and full cells.