A phosphorene–graphene hybrid material as ahigh.

1、A phosphorenegraphene hybrid material as a high-capacity anode for sodium-ion batteries Jie Sun1, Hyun-Wook Lee1, Mauro Pasta1, Hongtao Yuan2,3,Guangyuan Zheng4, Yongming Sun1,Yuzhang Li1 and Yi Cui1,3* Nature nanotechnology Sep 7,2015 Shaoxiang Li 2015.10.16 CONTENTS Sodium-ion batteries advantages

2、 : rich resource. challenges : anode materials with high specific capacity and appropriately low redox potential. traditional anode materials metallic sodium:dendrite formation,low melting point(98). graphite:electrochemically inactive,interlayer d(1.86)sodium-ion(2.04),but capacity 284 mAh g-1. Bac

3、kground Sodium-ion batteries advantages : rich resource. challenges : anode materials with high specific capacity and appropriately low redox potential. traditional anode materials metallic sodium:dendrite formation,low melting point(98). graphite:electrochemically inactive,interlayer d(1.86)sodium-

4、ion(2.04),but capacity 284 mAh g-1. Background Phosphorus high theoretical specific capacity of 2596 mAh g-1. Background allotropes White phosphorus : tetrahedral P4 molecules , highly reactive and toxic. Amorphous red phosphorus : anode material for LIBs and SIBs, poor electrical conductivity, mode

5、st cycle life and rate performance. Orthorhombic black phosphorus : stable, closely resembles graphite， good conductor of electricity，large interlayer channel size (3.08 ), poor cycling performance for SIBs. Conclusion It is therefore important to investigate the sodiation mechanism in order to opti

6、mize the performance of black phosphorus for use in SIBs. Figure 1 .Ex-situ XRD patterns of black phosphorus taken before charging and after charging down to different voltages. a, In wide range. b, Amplification of (002) diffraction peaks.c, Amplification of (004) diffraction peaks. Characterizatio

7、n #(002) #(004) black phosphorus (110) (103) Na3P Characterization The XRD spectra of black P anode after cycling. a, Before cycling. b,Discharged state after 30 cycles between 1.50.54 V.c, Discharged state after 1 cycle between 1.50.02V. Electrochemical performance of black phosphorus in different

8、voltage ranges. Reversible desodiation capacity for the first 30 galvanostatic cycles of the black phosphorus electrodes between different voltage ranges at a current density of 0.05 A g-1. 1.5-0.02V before cycling 1.5-0.54V Significant capacity loss upon cycling between 0.02-1.5V. Characterization

9、b, High-resolution and bright-field TEM image of black phosphorus before sodiation. ce, Time-lapse TEM images of sodiation in black phosphorus. Sodium ions transport along the x-axis channel, causing a volume expansion along the y-axis direction. Diagram Analysis full sodiation volume expansion 500%

10、 x axis expansion 0 y axis expansion 92% z axis expansion 160% Conclusion minimizing the width and the thickness of the black phosphorus layers would help reduce the stress built up along the critical y and z axial directions.monolayer black phosphorus (phosphorene). Characterization Figure .Structu

11、ral evolution of the sandwiched phosphorenegraphene structure during sodiation. Structure Benefits sandwiching small phosphorene layers between large graphene sheets. the ultrathin phosphorene minimizes the diffusion distance of both sodium ions and electrons enhanced rate performance the graphene l

12、ayers fast transport of electrons the space between phosphorene nanosheets elastic buffer Synthesis ultrasonication for 10 h(30） 20 ml N-methyl-2-pyrrolidone(NMP) centrifugation few-layer phosphorene 2 mg black phosphorus 2 mg graphite 20 ml N-methyl-2-pyrrolidone(NMP) ultrasonication for 30 min cen

13、trifugation graphene graphene and phosphorene mixed in NMPevaporating NMP 120 in a vacuum oven centrifugation dry at 80 phosphorene graphene hybrids Characterization Figure | Evidence of monolayer and few-layer phosphorene. a, TEM image of monolayer phosphorene. Scale bar, 2 m. b, TEM image of trila

14、yer phosphorene nanobelt showing the long side. Scale bar, 200 nm. Inset: HRTEM image of the edge. c, HRTEM image of selected area of b with measured lattice spacing. The HRTEM image in the inset to Fig. b shows a nanosheet made of three phosphorene layers with a 002 lattice spacing of 7.7 . Charact

15、erization Figure | Evidence of monolayer and few-layer phosphorene. e.AFM image of monolayer and few-layer phosphorene.Scale bar, 2 m. f.Measured thickness of the phosphorene in e. Thicknesses: rang between 0.84 and 4.22 nm. 1 to 5 phosphorene layers. Width: rang between 700 nm and 10 m. Characteriz

16、ation Figure | Evidence of monolayer and few-layer phosphorene. g, XRD pattern of black phosphorus and phosphorene. h, Amplification of XRD pattern of black phosphorus and phosphorene in the low-angle range (dashed rectangle in g). 002 lattice spacing 7.7 of phosphorene , larger than the 5.2 of blac

17、k phosphorus x and y channel sizes increase to 3.7 and 5.6 , opening the y channel to sodium ion (2.04 ) diffusion. Structure Characterization Figure | TEM and elemental dot-mapping images of phosphorene/graphene hybrid containing 48.3 wt% P. a, Bright-field TEM image of phosphorene/graphene composi

18、te (scalebar: 5 m). b, Dark-field TEM image of phosphorene/graphene composite (scale bar: 5 m). c, The corresponding selected area EELS elemental dot-mapping images of C and P elements. Phosphorene nanosheets uniformly distributed and sandwiched between the wider graphene nanosheets. Characterizatio

19、n Figure | Physical characterization of the phosphorenegraphene hybrid structure. b, TEM image of the phosphorenegraphene hybrid. Scale bar, 2 m. c, HRTEM image of the cross-section of the phosphorenegraphene hybrid (the turned-up right edge in b). Scale bar, 2 nm. Thickness of 25 nm, with alternati

20、ng phosphorene and graphene layers. d, Raman spectra of phosphorenegraphene hybrid with the modes of both phosphorene (A1g, A2g and B2g) and graphene (G and 2D). The intensity of the ratios A2g/A1g and A2g/B2g correspond to nanosheets made of five phosphorene layers or less. Characterization Characterization Figure a,b .Electrochemical characterization of graphene anode for sodium batteries. (0.02-1.5 V 0.05 A g-1 ） The contribution of graphene to the reversible capacity is negligible (40 mA h g1） Conclusion 1. We