Molten Salt-Shielded Synthesis(MS^(3))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 largescale 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(MS^(3))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 Ti_(3)C_(2)T_(x),Ti_(2)CT_(x),Ti_(3)CNT_(x),and Ti_(4)N_(3)T_(x),were successfully synthesized using the MS^(3) method.We also present the flexibility of the MS^(3) method by scaling the etching process to large batches of 20 and 60 g of Ti_(3)AlC_(2) MAX precursor in one pot.When used as negative electrodes,the prepared MS^(3)-MXenes delivered excellent electrochemical properties for high-rate Li-ion storage.