Theoretical Prediction of Janus TQ-Graphene as a Metallic Two-Dimensional Carbon Allotrope with Negative Poisson’s Ratios for High Capacity Sodium-Ion Batteries

Carbonaceous materials are considered the most promising anode materials for sodium-ion batteries (SIBs) due to their abundant active sites, high electronic conductivity, and good mechanical stability. However, two typical types of carbon materials, graphite and graphene, are unsuitable for Na storage arising from π-electron delocalization. The introduction of Janus structure in graphene can disrupt the extended sp2 conjugated network and thus enhance the surface reactivity. Herein, inspired by the dissymmetric structural characteristics of triquinacene, we construct a metallic two-dimensional Janus carbon allotrope, termed TQ-graphene. After confirming its dynamical, thermal, and mechanical stability, we find that TQ-graphene is an auxetic material with large in-plane negative Poisson's ratios. Furthermore, it exhibits excellent performance as an anode material for SIBs with an extremely high capacity of 2436 mA h g–1, a small diffusion barrier (0.01∼0.34 eV), and a low average voltage (0.32 V).