Unraveling the Atomistic Sodiation Mechanism of Black Phosphorus for Sodium Ion Batteries by First-Principles Calculations

Abstract

As opposed to the standard graphite anode used for lithium (Li) ion batteries (LIBs), a standard anode material for sodium (Na) ion batteries (NIBs) has not yet been reported. Black phosphorus is potentially very attractive as an anode material for NIBs, as it has a layered structure similar to graphite but a greater interlayer distance. In this work, we propose an atomistic mechanism for the sodiation of black phosphorus, based on first-principle calculations. The layered structure of black phosphorous is maintained up to the composition of Na 0.25 P, with one-dimensional sodiation (an intercalation process) occurring in the interlayer spaces of the black phosphorus, resulting in sliding of the phosphorene layers because one Na atom tends to bind to four P atoms. At Na levels beyond Na 0.25 P, the intercalation process changes to an alloying process. Sodiation exceeding the critical composition leads to breaking of P-P bonds and eventual formation of an amorphous phase from the layered Na x P structure. After the P-P bonds in the layered Na x P structure are broken, in a progress in which staggered P-P bonds are preferentially broken rather than planar P-P bonds, P 2 dumbbells are generated. As sodiation proceeds further, most of the P 2 dumbbells become isolated P atoms. Thus, in the amorphous Na 3 P phase, only low-coordinate P components such as isolated atoms (primarily) and dumbbells are found. We expect that our comprehensive understanding of the sodiation mechanism in black phosphorus will provide helpful guidelines in designing new types of black phosphorus anodes to obtain better performing NIBs.

Ab initio prediction of borophene as an extraordinary anode material exhibiting ultrafast directional sodium diffusion for sodium-based batteries

“…In this work, we comprehensively investigated the feasibility of employing borophene as anode material for sodiumbased batteries using density functional theory (DFT) method. The calculation results show that borophene can not only provide a superhigh capacity (1,218 mAh g -1 ), but also exhibit a directional ultrahigh sodium diffusivity, which is estimated to be more than a thousand times higher than that of conventional anode materials such as Na 2 Ti 3 O 7 [26] and Na 3 Sb [27] and one to seven magnitudes higher than other previously reported 2D materials [12][13][14][15][16][17][18][19]. The ultrahigh diffusivity will revolutionize the rate capability of sodium-based batteries.…”

“…The loose packing between the 2D layers can accommodate the volume expansion caused by the insertion of sodium atoms and maintain the structural integrity. Many 2D materials, such as defective/doped graphene [12,13], transition metal dichalcogenides (TMD) [14,15], transition metal carbides (MXenes) [16,17] and phosphorene [18,19], have been explored as potential candidates for the anode material of sodium-based batteries using first-principle method, and some of the predicted good performance have already been proven in experiments [20,21]. Recently, borophene, a 2D sheet of boron, has been successfully synthesized by Mannix et al [22].…”

Beyond Li-ion: electrode materials for sodium- and magnesium-ion batteries

“…Hembram et al [95] proposed an atomistic mechanism for the sodiation of black phosphorus based on first-principle calculations. It was determined that the sodiation of the layered spaces of black phosphorus induces changes in the layer stacking because of sliding of the phosphorene layers.…”

Recent advances in synthesis, properties, and applications of phosphorene

“…Recent DFT study of the intercalation of Na in BP 119 and few-layer phosphorene 118 has demonstrated a fast (energy barrier of 0.04 eV) and anisotropic (Fig. 6b) Na diffusion and, additionally, that phosphorene undergoes SMT at high Na intercalation concentration.…”