NbCT MXene as High-Performance Energy Storage Material with Na, K, and Liquid K-Na Alloy Anodes.

Two-dimensional MXenes perform well as hosts in batteries, which are promising for next-generation energy storage materials. With low price and high performance, sodium (Na) and potassium (K) own the potential to replace lithium in energy storage devices, but the larger radii and dendrite growth restrict their commercialization. Herein, we successfully synthesized an accordion-like NbCT MXene, whose crystal structure integrity and lamellar separation have been confirmed by characterization methods like high-resolution transmission electron microscopy (HR-TEM). Combined with solid Na and K and liquid K-Na alloy as anodes, the NbCT MXene shows excellent electrochemical performance, such as high capacity retention after large current shock in tests of rate performance and long time stability for more than 500 cycles, etc. Also, the NbCT MXene coupled with liquid K-Na anode performs better than that coupled with solid K for the dendrite-controlling character of the liquid electrode. The NbCT MXene would boost the exploitation of more suitable host materials for Na/K-ion batteries and promote an in-depth understanding of MXenes.