Non-hexagonal tetra-hexa-octa-graphene for high-performance sodium-ion battery anodes: Effects of structural topology, mechanical strain, and van der Waals coupling

Although numerous freestanding monolayer carbon allotropes have been proposed as anode candidates for sodium-ion batteries (SIBs), the influence of substrate-induced lattice strain and interfacial van der Waals interactions on their electrochemical performance remains largely unexplored. Using first-principles calculations, we predict a carbon allotrope, THO-graphene, composed of tetra-, hexa-, and octa-carbon rings, which exhibits an indirect bandgap semiconducting behavior. Monolayer THO-graphene demonstrates a high Na storage capacity (1340.05 mAh g⁻¹), a low diffusion barrier (0.35 eV), and a low average open-circuit voltage (0.12 V), highlighting its potential as an anode material for SIBs. Remarkably, uniaxial strain ranging from −6 % to 6 % triggers a semiconductor-to-metal transition in THO-graphene, boosting its electrical conductivity while introducing anisotropic Na adsorption characteristics and reducing the diffusion barrier to an ultralow value of 0.14 eV. Furthermore, the inherently metallic bilayer THO-graphene enhances Na adsorption capability and preserves rapid diffusion kinetics.