Opening Magnesium Storage Capability of Two-Dimensional MXene by Intercalation of Cationic Surfactant

Two-dimensional (2D) Ti₃C₂ MXene has attracted great attention in electrochemical energy storage devices (supercapacitors and lithium-ion and sodium-ion batteries) due to its excellent electrical conductivity as well as high volumetric capacity. Nevertheless, a previous study showed that multivalent Mg²⁺ ions cannot reversibly insert into MXene, resulting in a negligible capacity. Here, we demonstrate a simple strategy to achieve high magnesium storage capability for Ti₃C₂ MXene by preintercalating a cationic surfactant, cetyltrimethylammonium bromide (CTAB). Density functional theory simulations verify that intercalated CTA⁺ cations reduce the diffusion barrier of Mg²⁺ on the MXene surface, resulting in the significant improvement of the reversible insertion/deinsertion of Mg²⁺ ions between MXene layers. Consequently, the MXene electrode exhibits a desirable volumetric specific capacity of 300 mAh cm^-3 at 50 mA g^-1 as well as outstanding rate performance. This work endows MXene material with an application in electrochemical energy storage and, simultaneously, introduces magnesium battery materials as a member.