Mxene-derived bilayered vanadium oxides with enhanced stability in Li-ion batteries

Abstract

Bilayered vanadium oxides (BVOs) are a high-capacity intercalation host with affinity for various ions in energy storage systems. However, the electrochemical stability of BVOs upon extended galvanostatic cycling, especially at high rates, is lackluster. In this study, we demonstrate a transformative synthesis of chemically preintercalated BVOs with unique two-dimensional (2D) morphology and improved electrochemical stability by oxidation of V2CTx MXenes in hydrogen peroxide in the presence of alkali and alkaline-earth metal chlorides. The structure and composition of V2CTxderived δ-MxV2O5·nH2O (M = Li, Na, K, Mg, and Ca) phases were examined by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The electrochemical properties of the V2CTx-derived δ-LixV2O5·nH2O and δ-MgxV2O5·nH2O electrodes in Li-ion cells were studied. Both materials exhibited high reversible specific capacity, improved cycling stability, and excellent rate capability. Notably, an enhanced tolerance to high current rates is observed with specific discharge capacity dropping from 200 to 130 mAh·g−1 and from 192 to 146 mAh·g−1 when the current rate was changed from C/10 to 5C in the case of V2CTx-derived δ-LixV2O5·nH2O and δ-MgxV2O5·nH2O electrodes, respectively. The improved capacity retention during electrochemical cycling may be attributed to the 2D morphology and improved crystallinity of the material enabled by the synthesis route.