A phosphorene–graphene hybrid material as a high-capacity anode for sodium-ion batteries

Abstract

Sodium-ion batteries have recently attracted significant attention as an alternative to lithium-ion batteries because sodium sources do not present the geopolitical issues that lithium sources might. Although recent reports on cathode materials for sodium-ion batteries have demonstrated performances comparable to their lithium-ion counterparts, the major scientific challenge for a competitive sodium-ion battery technology is to develop viable anode materials. Here we show that a hybrid material made out of a few phosphorene layers sandwiched between graphene layers shows a specific capacity of 2,440 mA h g(-1) (calculated using the mass of phosphorus only) at a current density of 0.05 A g(-1) and an 83% capacity retention after 100 cycles while operating between 0 and 1.5 V. Using in situ transmission electron microscopy and ex situ X-ray diffraction techniques, we explain the large capacity of our anode through a dual mechanism of intercalation of sodium ions along the x axis of the phosphorene layers followed by the formation of a Na3P alloy. The presence of graphene layers in the hybrid material works as a mechanical backbone and an electrical highway, ensuring that a suitable elastic buffer space accommodates the anisotropic expansion of phosphorene layers along the y and z axial directions for stable cycling operation.

Emerging Trends in Phosphorene Fabrication towards Next Generation Devices

“…The NMP solvent for obtaining stable, highly concentrated (≈0.4 mg mL –1 ) BP dispersions was used in LPE in most of the reported studies 12, 67, 85, 91, 95, 118, 160, 166, 183, 185, 186, 187. NMP and DMF are well suit for liquid exfoliation owing to their relatively high boiling points and surface tension (≈40 mJ m –2 ) 166, 183, 188.…”

2D Black Phosphorus: from Preparation to Applications for Electrochemical Energy Storage

“…The transport properties of anisotropic sodium ions within 2D BP were also investigated along in situ aberration‐corrected TEM and DFT simulations, which confirmed the migration of sodium ions along the [100] directions (Figure 18b,c) 219. Recently, Sun et al fabricated a 2D BP–graphene sandwich structure via self‐assembly by mixing NMP dispersions of FLP and graphene 105. The results showed that a low carbon–phosphorus mole ratio was beneficial to specific capacity because graphene was electrochemically inactive for sodiation.…”

“…Bulk BP has been successfully exfoliated using several solvents. Organic solvents, including N ‐methyl‐2‐pyrrolidone (NMP),101, 103, 104, 105, 106, 107 N ‐cyclohexyl‐2‐pyrrolidone (CHP),108 dimethylformamide (DMF),109, 110 dimethyl sulfoxide,110, 111 and acetone,112, 113 have been used to prepare uniform and stable dispersions. Among these solvents, NMP (40 mJ m −2 ) and DMF (37.1 mJ m −2 ) have surface energy values that are close to the exfoliation criterion of 2D BP (35–40 mJ m −2 ) 114.…”

“…BP has a layered structure similar to that of graphite, but BP has a greater interlayer channel size (3.08 vs 1.86 Å in graphite), which implies that sodium can be stored between the 2D BP layers 105. The strong binding energy in sodium–2D BP suggested that sodium can be stabilized on the surface of 2D BP without clustering 217.…”

“…Recently, 2D BP with various layers (from 2 to 11) was investigated as an anode material in SIBs and showed a high capacity of 1968 mA h g −1 at a current density of 100 mA g −1 134. Sun et al105 investigated the sodiation mechanism of BP by using in situ TEM and ex situ XRD techniques. A two‐step sodiation process of intercalation and alloying was demonstrated, which agreed well with theoretical prediction.…”