Surface Electrochemical Stability and Strain-Tunable Lithium Storage of Highly Flexible 2D Transition Metal Carbides

2D transition metal carbides and/or nitrides (MXenes) have attracted enormous attention because of their potential applications in energy storage, catalysis, and others. The control of surface terminations is generally believed to offer the potential preparation approaches to novel MXenes, while an external strain may provide solution to property modification. However, an atomistic understanding on the stabilization of surface complexity and the influence of strain on electrochemical properties of MXenes are scarce yet much demanded. Herein, taking Ti2CTn as a representative MXene, the thermodynamically favorable configurations are explored with a mixture of functional groups under various electrochemical environments. It predicts that five thermodynamically preferable Ti2CTn terminated by O-and F-cofunctionalized groups are discovered, all of which show excellent mechanical flexibility and strength that appear a decreasing trend as increasing F/O ratio. Further investigations on strain-controllable Li-transport of these cofunctionalized Ti2CT2 indicate that a mixture of surface terminations decreases the diffusion barriers, while the uniaxial strain modifies the diffusion pathways of Li atom owing to asymmetrical surface geometry and electronic polarization. These findings provide a view on the modification of properties by controlling surface complexity, demonstrating effective pathways in designing MXenes by electrochemical approach and tuning electrochemical property by strains.