Interlayer spacing enlarged 2D 1T-MoS2 and V2CTx MXene as superior anodes for boosting potassium-ion diffusion coefficient

Abstract

Two-dimensional (2D) materials used in potassium ion batteries (PIBs) have high theoretical capacitance and excellent rate characteristics. However, the origin of low diffusion of potassium ions and poor storage kinetics still remain challenge mainly due to the large size of potassium ions (0.138 nm) and narrow 2D interlayer spacing. Herein, the V2CTx-based hybrids including 1T-MoS2 (1T -MoS2@V2CTx) has been successfully constructed by the magneto-hydrothermal method and proved to be an eminent anode, which can make PIBs have high reversible capacity and eminent rate performance at the same time. Moreover, the combination of 2D 1T-MoS2 and V2CTx not only significantly promotes the transfer of interfacial charges as well as accelerates the transmission and diffusion of electrons and K+, but also helps to alleviate the volume changes caused by the insertion/extraction of large-sized K+ during the cycle, which makes the electrode exhibit good cycle stability. Density functional theory (DFT) indicates that the synergy effect between 1T-MoS2 and V2CTx has significantly strengthened the potassium affinities and ion diffusion kinetics in the 1T-MoS2@V2CTx anode by reducing the ion diffusion energy barrier, thereby showing outstanding K+ storage performance, especially in 1T-MoS2@V2CF2. As a result, the 1T-MoS2@V2CTx anode shows a high reversible capacity of 887.3 mA h g−1 at 0.1 A g−1, eminent rate performance of the capacity maintaining 563.6 mA h g−1 at 2.0 A g−1 and remarkable cycle stability of 601.2/374.7 mA h g−1 with 69.4/56.5% capacity retention after 2000 cycles at 1.0/2.0 A g−1. This work provides a new way for the exquisite design of 2D composite electrodes with excellent performance in PIBs.