ABSTRACT
MXenes are emerging 2D materials that have gained great attention because of their unique physical-chemical properties. However, the wide application of MXenes is prohibited by their high cost and environmentally harmful synthesis process. Here a fluoride- and acid-free physical vacuum distillation strategy is proposed to directly synthesize a series of MXenes. Specifically, by introducing a low-boiling-point element into MAX and subsequently evaporating A elements via physical vacuum distillation, fluoride-free MXenes (Ti3C2Tx, Nb2CTx, Nb4C3Tx, Ta2CTx, Ti2NTx, Ti3CNTx, etc.) are fabricated. This is a green and one-step process without any acid/alkaline involved and with all reactions inside a vacuum tube furnace, avoiding any contamination to external environments. Besides, the synthetic temperature is controlled to regulate the layered structures and specific surface areas of MXenes. Accordingly, the synthesized Ti3C2Tx MXene exhibits improved sodium storage performance. This method may provide an alternative for the scalable production of MXenes and other 2D materials.
ABSTRACT
Aqueous zinc (Zn)-ion batteries are regarded as promising candidates for large-scale energy storage systems because of their high safety, low cost, and environmental benignity. However, the dendrite issue of Zn anode hinders their practical application. Herein, a freestanding, lightweight, and zincophilic MXene/nanoporous oxide heterostructure engineered separator is designed to stabilize a Zn metal anode. The nanoporous oxides prepared by a one-step vacuum distillation technique afford the advantages of large surface area, high porosity, and homogeneous porous structure. The zincophilic MXene@oxides layer can homogenize the electric field distribution, facilitate ion diffusion kinetics, reduce local current density, and promote even Zn ionic flux, which will regulate uniform Zn deposition and suppress side reactions. Accordingly, dendrite-free Zn anodes with stable cyclability are achieved for over 500 h at an ultrahigh area capacity of 10 mAh cm-2. Besides, flexible, long-lifespan, and high-rate N/S-doped three-dimensional MXene@MnO2||Zn full cells are constructed with the engineered separator. Moreover, this strategy can be successfully extended to lithium, sodium, potassium, and magnesium metal batteries, indicating that separator regulation is a universal approach to overcome the challenges of metal batteries.
