Flexible two-dimensional Tin+1Cn (n = 1, 2 and 3) and their functionalized MXenes predicted by density functional theories

Two-dimensional (2D) transition metal carbides/nitrides Mn+1Xn labeled as MXenes are attracting increasing interest due to promising applications as Li-ion battery anodes and hybrid electro-chemical capacitors. To realize MXenes devices in future flexible practical applications, it is necessary to have a full understanding of the mechanical properties of MXenes under deformation. In this study, we extensively investigated the stress–strain curves and the deformation mechanisms in response to tensile stress by first principles calculations using 2D Tin+1Cn (n = 1, 2 and/or 3) as examples. Our results show that 2D Ti2C can sustain large strains of 9.5%, 18% and 17% under tensions of biaxial and uniaxial along x and y, respectively, which respectively increase to 20%, 28% and 26.5% for 2D Ti2CO2 due to surface functionalizing oxygen, which is much better than graphene (15% biaxial). The failure of 2D Tin+1Cn MXene is due to the significant collapse of the surface atomic layer; however, surface functionalization could slow down this collapse, resulting in the improvement of mechanical flexibility. We have also discussed the critical strains and Young's modulus of 2D Tin+1Cn and Tin+1CnO2. Our results provide an insight into the microscopic deformation mechanism of MXenes and hence benefit their applications in flexible electronic devices.