Surface modification and in situ carbon intercalation of two-dimensional niobium carbide as promising electrode materials for potassium-ion batteries

Abstract

Potassium ion batteries (KIBs) have a great potential in large scale energy storage because of their cost advantages and similar working mechanism to lithium ion batteries (LIBs). However, the larger ionic radius of K+ presents great challenges to find suitable electrode materials for K+ insertion/extraction. Herein, the surface-modified and in-situ carbon-intercalated Nb2CTx MXene is rationally designed and synthesized as electrode for KIBs. The as-prepared Nb2C/C has larger effective interlayer distance (i.e. gallery height), higher specific surface area and electrical conductivity, and lower concentration of surface functional groups. As a result, Nb2C/C exhibits a significantly increased coulombic efficiency (67.6% for Nb2C/C, 28.5% for Nb2CTx) and its specific capacity is two times higher than that of Nb2CTx at 0.02 A·g−1, three times at 0.1 A·g−1. The Nb2C/C delivers an initial specific capacity of 397.9 mAh·g−1 at 0.02 A·g−1 and 338.1 mAh·g−1 at 0.1 A·g−1, and maintains 80.0% after 100 cycles at 0.02 A·g−1 and 76.2% after 200 cycles at 0.1 A·g−1, respectively. Notably, Nb2C/C possesses outstanding cyclic stability and rate performance at various current densities, outperforming most of reported MXene-based anodes for KIBs. The excellent potassium storage performance of Nb2C/C can be ascribed to the abundant active sites exposed to electrolyte, rapid diffusion kinetics of K+ and few side reactions at the electrode/electrolyte interface. This work proposes an effective strategy for the MXene-based materials to maximize their potential applications in various fields such as batteries, supercapacitors and catalysts.