Collaborative activation mechanism in double transition metal MXenes anode: An effective method to improve the capacitance of sodium ion battery

Through theoretical calculations, it is found that anode materials with double transition metal terminals (VNbC, VTaC, and NbTaC) exhibit better performance than their single metallic phases. Compared with single metal phase, the maximum sodium adsorption capacities of VNbC, VTaC, and NbTaC increased by 75%, 37.5%, and 75%, respectively. In particular, the metal VNbC VTaC and NbTaC anodes not only have high theoretical capacitances of 601.85, 302.20 and 328.13 mAhg⁻¹, but also have original low migration barriers with sodium atoms. Bader charge indicates that the large capacities originate from the difference in metal electronegativity, and this difference leads to a reduction in the charge contribution of transition metals in materials and the accumulation of excess electrons on the surface. These extra accumulated electrons can be transferred to the outside to form an additional negative electron cloud that stabilizes the formation of the second layer of sodium adsorption, and leading to a large theoretical capacitance. We named this phenomenon the “Collaborative Activation” mechanism of double transition metal MXenes. These interesting results show that MXene anodes composed of different metal terminals are powerful methods to improve anode performance. Therefore, it provides a powerful reference for the research of MXenes.