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

Potassium ion batteries (KIBs) have a great potential in large scale energy storage because of their cost advan-tages 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 Nb2CT(x) 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 & BULL;g(-1), three times at 0.1 A & BULL;g(-1). The Nb2C/C delivers an initial specific capacity of 397.9 mAh & BULL;g(-1) at 0.02 A & BULL;g(-1) and 338.1 mAh & BULL;g(-1) at 0.1 A & BULL;g(-1), and maintains 80.0% after 100 cycles at 0.02 A & BULL;g(-1) and 76.2% after 200 cycles at 0.1 A & BULL;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 elec-trode/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.

Automated summary

Surface-modified and in-situ carbon-intercalated Nb2CT(x) MXene electrode for potassium ion batteries shows larger effective interlayer distance, higher specific surface area, and electrical conductivity, leading to significantly increased coulombic efficiency and specific capacity compared to unmodified Nb2CTx.