Two-dimensional TTH-graphene: Structural, defective, and interfacial engineering on anode materials for potassium-ion batteries

Potassium-ion batteries (PIBs) demonstrate significant potential for future renewable energy storage systems, given the high natural richness and economic benefits of potassium resources. Nevertheless, the primary challenge hindering the development of PIBs is the scarcity of appropriate anode materials capable of delivering high performance. Using first-principles calculations, we theoretically design a two-dimensional graphene allotrope, termed TTH-graphene, constructed from assembled tetracyclo[6.6.0.02,6.010,14]tetradeca-1(8),2,4,6,9,11,13-heptaene (C14H8) structural units, which demonstrates good dynamical, thermal, and mechanical stability. The non-hexagonal symmetry can enhance the surface reactivity, making TTH-graphene a high-performance anode for PIBs with a low K migration barrier (0.22 eV), a moderate average open-circuit voltage (0.42 V), a high theoretical capacity (956.33 mA h g−1), and a small lattice expansion (1.2%). Furthermore, the appearance of vacancy defects enhances the K adsorption strength but induces the decrease in ionic diffusivity. Compared with the monolayer, the TTH-graphene bilayer exhibits an enhancement of the adsorption and diffusion performance of K on the outer surface.