Honeycomb-kagome FSL-graphene: A carbon allotrope as an ultra-high capacity anode material for fast-rechargeable sodium-ion battery

Sodium-ion batteries (SIBs) are promising candidates for large-scale energy storage due to the abundance and low cost of sodium. However, graphite, the primary anode for commercial lithium-ion batteries, cannot be applied to SIBs. Its two-dimensional (2D) counterpart graphene is also inactive toward Na ions because of the delocalized π-electron network. We propose an idea to tackle this problem by introducing kagome topology into the honeycomb lattice, creating localized electronic states for improving the Na storage performance. Herein, we design a form of 2D carbon allotrope (named FSL-graphene), consisting of a kagome and a honeycomb sublattice. It has excellent stability, which is confirmed by the superior cohesive energy, positive phonon modes, high thermal stability, and strong mechanical stability. FSL-graphene exhibits an ultra-high theoretical Na storage capacity of 3347.1 mA h g−1, superior to most previously reported 2D anode materials. In addition, it possesses low diffusion energy barriers (0.19–0.23 eV), low open-circuit voltages (0.59–0.61 V), and small changes in lattice constants (1.3%). Furthermore, the electrolytes with high dielectric constants (e.g., ethylene carbonate) could improve the adsorption and migration of Na on FSL-graphene. This study provides an insight for designing high-performance carbon anode materials for SIBs by focusing on the topological lattices.