In situ built nanoconfined Nb2O5 particles in a 3D interconnected Nb2C MXene@rGO conductive framework for high-performance potassium-ion batteries

Exploring novel anode materials with excellent electrochemical performance is of great significance for the development of potassium-ion batteries (KIBs). Here, a 3D interconnected Nb2C/rGO conductive framework with in situ generated Nb2O5 nanoparticles (Nb2O5/Nb2C/rGO) is successfully constructed by a simple one-step hydrothermal method and subsequent freeze-drying and annealing treatments. The unique structure formed by the intimate contact of the three components has a 3D conductive network, abundant pores and a large specific surface area, which can not only inhibit the self-restacking of Nb2C nanosheets and the agglomeration of Nb2O5 nanoparticles and alleviate the volume change during the charge–discharge process, but also expose more active sites and provide unimpeded channels for the diffusion of K+ and infiltration of the electrolyte. Meanwhile, Nb2O5 nanoparticles produced by in situ oxidation of surface Nb2C and the residual subsurface Nb2C with a low potassium ion diffusion barrier and a high conductivity can shorten the diffusion distance and promote the diffusion kinetics of electrons/ions. Benefiting from the elaborately designed structure and synergistic effects of three different components, as an anode for KIBs, the resulting Nb2O5/Nb2C/rGO exhibits a superior specific capacity of 410.6 mA h g−1 after 100 cycles at 0.1 A g−1, an exceptional rate performance of 159.0 mA h g−1 at 5 A g−1, a capacity retention of 88.8% and a coulombic efficiency over 99.8% after 1000 cycles at 2.0 A g−1. Moreover, Nb2O5/Nb2C/rGO also shows a good potassium storage performance in a KIB full-cell. Furthermore, the combined potassium storage mechanism of K+ intercalation/deintercalation is revealed by CV and in/ex situ analyses. This work can provide more meaningful guidance for the rational design and construction of anode materials for high-performance KIBs.