Atomistic Sodiation Mechanism of a Phosphorene/Graphene Heterostructure for Sodium-Ion Batteries Determined by First-Principles Calculations

Black phosphorus has recently attracted significant attention as an anode material for sodium-ion batteries (SIBs); however, the material suffers from a severe volume change during charge/discharge processes, leading to poor cycle life. To overcome this drawback of black phosphorus, a phosphorene/graphene (P/G) heterostructure was recently proposed, but no atomistic understanding of the sodiation mechanism has yet been reported. In this work, we report an atomistic mechanism for the sodiation of the P/G hybrid material based on first-principles calculations. The layered structure of P/G is maintained up to the composition of Na0.25P/G, which can be referred to as an intercalation process; however, above that composition, further sodiation leads to the dissociation of P−P bonds and the formation of an amorphous NaxP/G structure where the graphene layers are not broken and no Na atoms intercalate into the spaces between two graphene layers, which is referred to as an alloying process. According to our first...