Quasi Three-Dimensional Tetragonal SiC Polymorphs as Efficient Anodes for Sodium-Ion Batteries

In the present work, we investigate, for the first time, quasi 3D porous tetragonal silicon-carbon polymorphs t(SiC)(12) and t(SiC)(20) on the basis of first-principles density functional theory calculations. The structural design of these q3-t(SiC)(12) and q3-t(SiC)(20) polymorphs follows an intuitive rational approach based on armchair nanotubes of a tetragonal SiC monolayer where C-C and Si-Si bonds are arranged in a paired configuration for retaining a 1:1 ratio of the two elements. Our calculations uncover that q3-t(SiC)(12) and q3-t(SiC)(20) polymorphs are thermally, dynamically, and mechanically stable with this lattice framework. The results demonstrate that the smaller polymorph q3-t(SiC)(12) shows a small band gap (similar to 0.59 eV), while the larger polymorph of q3-t(SiC)(20) displays a Dirac nodal line semimetal. Moreover, the 1D channels are favorable for accommodating Na ions with excellent (>300 mAh g(-1)) reversible theoretical capacities. Thus confirming potential suitability of the two porous polymorphs with an appropriate average voltage and vanishingly small volume change (<6%) as anodes for Na-ion batteries.