Design of an aluminium ion battery with a graphyne host: lowest volume expansion, high stability and low diffusion barriers

Commercialization of aluminium ion battery (AIB) requires limited volume expansion of the host cathode materials after AlCl4 intercalation, lower activation barrier, high theoretical specific capacity (TSC), cyclic durability and thermodynamic stability. Most of the carbon and non-carbon based cathode hosts explored so far failed to address the issue of volume expansion and there is a lack of clarity about thermodynamic stability. In this work, we employed multipronged first principles computational approaches on alpha- and gamma-graphyne (GY) and showed that alpha-GY as a promising cathode host addresses each of the above concerns. Both alpha and gamma-GYs provide ample space to accommodate more number of AlCl4 molecules leading to a high TSC of 186 mA h g(-1) and open circuit voltages of 2.18 and 2.22 V, respectively. The absence of bond dissociation of AlCl4 and deformation of GY sheets at 300 and 600 K, as revealed by ab initio molecular dynamics (AIMD) simulation, indicates the stability of alpha- and gamma-GY with adsorbed AlCl4. alpha-GY after intercalation shows a volume expansion of 186% which is the lowest among the cathode materials studied so far. The negligible expansion energy per unit surface area (similar to 0.003 eV angstrom(-2)) ensures the reversibility and hence cyclic durability of alpha-GY. Although the gamma-GY shows a volume expansion of 249%, it is still promising. The NEB based diffusion study on monolayer and bilayer GY estimates the activation barriers to be (0.26, 0.06 eV) and (0.42, 0.16 eV) for alpha and gamma phases, respectively. These values are either comparable to or lower than those of earlier reported cathode hosts.

Automated summary

This study proposes a solution for the commercialization of aluminium ion batteries by using alpha-graphyne (alpha-GY) as the cathode host material. Alpha-GY exhibits the lowest volume expansion, high theoretical specific capacity, and lower activation barrier among the cathode materials studied. Although gamma-graphyne (gamma-GY) has a higher volume expansion, it still shows promising properties. The computational and simulation results demonstrate the stability, reversibility, and cyclic durability of alpha-GY with adsorbed AlCl4.