Molten Salt-Shielded Synthesis (MS³) of MXenes in Air

MXenes are two-dimensional transition metal carbides and/or nitrides with unique physiochemical properties and have attracted extensive interest in numerous fields. However, current MXene synthesis methods are limited by hazardous synthesis conditions, high production costs, or difficulty in large-scale production. Therefore, a general, safe, cost-effective, and scalable synthesis method for MXenes is crucial. Here, we report the fast synthesis of MXenes in the open air using a molten salt-shielded synthesis (MS³) method, which uses Lewis-acid salts as etchants and a low-melting-point eutectic salt mixture as the reaction medium and shield to prevent MXene oxidation at high temperatures. Carbide and nitride MXenes, including Ti₃C₂T_x, Ti₂CT_x, Ti₃CNT_x, and Ti₄N₃T_x, were successfully synthesized using the MS³ method. We also present the flexibility of the MS³ method by scaling the etching process to large batches of 20 and 60 g of Ti₃AlC₂ MAX precursor in one pot. When used as negative electrodes, the prepared MS³-MXenes delivered excellent electrochemical properties for high-rate Li-ion storage.