Adsorption and diffusion properties of calcium ions at the van der Waals interface of NbSe2-graphene 2D heterostructure for multivalent battery applications: density functional theory calculations

Multivalent-ion batteries such as calcium-ion batteries show promise as a high-density alternative to lithium-ion batteries which currently dominate the portable electronics market. In this work, the adsorption and diffusion properties of calcium ion at the van der Waals (vdW) interface of the 2D heterostructure formed by vertically stacking NbSe2 monolayer and graphene were investigated via density functional theory (DFT) calculations. Results showed that calcium can be effectively adsorbed on the vdW interface of the 2D heterostructure, with the binding energy of most stable site at -2.77 eV, much higher than most metal ions' binding on pristine graphene. Thus, the NbSe2-graphene 2D heterostructure reinforced the binding of calcium ions at the interface. It is revealed that due to the random stacking nature of NbSe2 and graphene, a multi-path minimum energy pathways were identified at the van de Waals region, with relatively low diffusion barriers of around 0.20-0.50 eV. These indicate the capabilities of the 2D vdW heterostructure for fast multivalent ionic mobility and charge-discharge rate, while maintaining strong binding at the vdW interface. The results reveal NbSe2-graphene 2D vdW heterostructure's potential as a promising anode material for multivalent battery applications.