Graphdiyne—A Two-Dimensional Cathode for Aluminum Dual-Ion Batteries with High Specific Capacity and Diffusivity

Abstract

Identifying a suitable cathode material for aluminum dual-ion batteries (ADIBs) with an enhanced specific capacity, cyclic durability, and open circuit voltage is among the major challenges in its commercialization. This study presents a graphdiyne (GDY) monolayer, a recently synthesized carbon allotrope, as a promising cathode material to host the diffusing AlCl4–, which is responsible for the charging/discharging process in ADIBs. Density functional theory calculations are performed to reveal the mechanism of adsorption of AlCl4 on GDY, while thermodynamical stability and diffusion dynamics are examined through ab initio molecular dynamics simulations. The theoretical specific capacity of this room-temperature stable system is calculated to be 186 mA h/g, which is 3 times higher compared to the case in which graphite is used as the cathode. The cyclic durability of this system is established as the GDY regains its equilibrium structure after releasing AlCl4 during discharge. The activation barrier—a measure of ease with which the diffusion occurs—is calculated with the aid of the climbing image-nudged elastic band method and found to be 0.08 and 0.05 eV for monolayer and bilayer GDY, respectively. Hence, with GDY as the cathode material, we can achieve an ultralow diffusion energy barrier. Furthermore, due to charge transfer between Cl and C sites, the semiconducting GDY becomes metallic upon AlCl4 adsorption, which is an added advantage in improving the electronic conductivity.