TiC3 Monolayer with High Specific Capacity for Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) have attracted considerable attention due to the intrinsic safety and high abundance of sodium. However, the lack of high-performance anode materials becomes a main obstacle for the development of SIBs. Here, we identify an ideal anode material, a metallic TiC3 monolayer with not only remarkably high storage capacity of 1278 mA h g-1 but also low barrier energy and open-circuit voltage, through first-principles swarm-intelligence structure calculations. TiC3 still keeps metallic after adsorbing two-layer Na atoms, ensuring good electrical conductivity during the battery cycle. Besides, high melting point and superior dynamical stability are in favor of practical application. Its excellent performance can be mainly attributed to the presence of an unusual n-biphenyl unit in the TiC3 monolayer. High cohesive energy, originating from multibonding coexistence (e.g., covalent, ionic, and metal bonds) in the TiC3 monolayer, provides strong feasibility for experimental synthesis. In comparison with TiC3, functionalized TiC3 with oxygen shows a higher storage capacity; meanwhile, it keeps nearly the same barrier energy. This is in sharp contrast with metal-rich MXenes. These intriguing properties make the TiC3 monolayer a promising anode material for SIBs.