NiX₂(X = S, Se, and Te) Monolayers: Promising Anodes in Li/Na-Ion Batteries and Superconductors

Based on the density functional theory calculations, we report the stability, electron structure, and potential applications in single-layer (SL) NiX₂(X = S, Se, and Te) that show high thermal, dynamical, and mechanical stability and possess ultralow isotropic Young's modulus. Moreover, these NiS₂, NiSe₂, and NiTe₂monolayers have high energy storage capacities of 874, 496, and 342 mA h g^-1and low diffusion energy barriers of 0.23/0.24/0.27 and 0.12/0.13/0.12 eV when used as anodes in lithium-ion batteries and sodium-ion batteries, respectively. SL NiS₂and NiSe₂show semiconducting traits in their freestanding crystals. Specifically, the 2D NiTe₂monolayer is determined to be an intrinsic superconductor with a transition temperature (T_c) of ∼2.24 K. The T_ccan be improved to 5.48 K when subjected to an in-plane compressive strain of 6%. These results enrich the family of transition metal-based 2D materials with multifunctionality and facilitate further experimental efforts toward next-generation nanodevices.