Hierarchical MoS₂–carbon porous nanorods towards atomic interfacial engineering for high-performance lithium storage

Abstract

Hierarchical nanostructures have attracted considerable attention for rechargeable battery systems since they combine the benefits of size effects induced by nanoscaling with the integrity of bulk materials. Despite significant progress, the hierarchical structures reported so far are designed only down to the nanoscale. To improve the battery performance, downsizing the designed building blocks of the hierarchical structure to smaller scales (molecular or even atomic level) is essential. This novel concept has been realized in a MoS 2 /C composite system, where MoS 2 and N-doped carbon molecular layers are alternately stacked to form nanosheet building blocks, which are further assembled into a porous nanorod structure. This hierarchical heterostructure converts the guiding principle of sub-nanoscale engineering into practice, aiming at increasing the interfaces between MoS 2 and carbon towards the largest possible molecular contact level. The resultant MoS 2 /N-doped carbon porous nanorods (MoS 2 / NC-PNR) electrode exhibits outstanding performances in lithium-ion batteries including high initial discharge capacity of $1300 mA h g À1 , cycling stability for 700 cycles and excellent rate performance (443 mA h g À1 at 10C). The outstanding performance of the MoS 2 /NC-PNR superstructure illustrates the enormous potential of the hierarchically designed 2D compounds from molecular layer level, which could be extended to other layered materials. Fig. 5 Structural organisation of MoS 2 /NC-PNR on several length scales: (a, c) SEM images (scale bar 1 mm), (b, d) TEM images (scale bar 100 nm), (e) HR-TEM images (scale bar 10 nm), (f) line scan of the white arrow in (e) and (g) schematic illustration of the hierarchical structure. 7558 | J. Mater. Chem. A, 2019, 7, 7553-7564 This journal isFig. 7 Electrochemical performance of MoS 2 /NC-PNR: (a) CV, (b) GCPL measurements at specific cycles, (c) cycling stability at 0.5C and the comparison with S-MoS 2 , (d) rate capability and (e) long-term cycling stability at 2C (activated at 0.2C for 10 cycles). 7560 | J. Mater. Chem. A, 2019, 7, 7553-7564 This journal is

Engineering Hollow Porous Carbon-Sphere-Confined MoS2 with Expanded (002) Planes for Boosting Potassium-Ion Storage

“…The overall survey spectrum (Figure a) of MoS 2 @HPCS includes C, N, O, Mo, and S, with contents of 61.68, 10.72, 4.61, 6.61, and 16.38 at%, respectively. The Mo/S mole ratio of MoS 2 @HPCS lower than 1/2 may originate from the surface defects of MoS 2 and the introduction of the S atom into HPCS. , The C 1s spectrum (Figure b) of high-resolution of MoS 2 @HPCS could fit well into two peaks of C–C (284.8 eV) and C–O (286.3 eV) . Two typical peaks at 231.8 and 229.9 eV, which correspond to Mo 3d 5/2 and Mo 3d 3/2 in Figure c, respectively, point to Mo 4+ .…”

Few‐Layered MoxW1−xS2‐Modified CdS Photocatalyst: One‐Step Synthesis with Bifunctional Precursors and Improved H2‐Evolution Activity

“…For the Mo element, the MoS 2 /CdS and Mo x W 1− x S 2 /CdS samples show distinct Mo 3 d 5/2 (228.5 eV) and Mo 3 d 3/2 (231.6 eV) peaks that are indexed to the Mo (IV) in MoS 2 and Mo x W 1− x S 2 cocatalysts compared with the conventional CdS, whereas the unavoidable oxidation of the cocatalyst leads to the presence of the Mo (VI) peaks (Mo 3 d 5/2 in 232.5 eV and Mo 3 d 3/2 in 235.6 eV). [ 62–66 ] Noticeably, it is worth mentioning that the intensity of the Mo (IV) peaks undergoes a dramatic decline after introducing W into the Mo x W 1− x S 2 /CdS photocatalyst, evidently implying the successful integration of W into the Mo x W 1− x S 2 cocatalyst (Figure 4B). For further investigation of W element, the W 4 f core‐level spectrum of the Mo x W 1− x S 2 /CdS photocatalyst is shown in Figure 4C.…”

MoS2 Nanotubes via Ionic-Liquid-Assisted Assembly of MoS2 Nanosheets for Lithium Storage

“…The second cathodic peak around ∼0.5 V can be assigned to the subsequent conversion reaction between MoS 2 and Li + , forming Li 2 S and metallic Mo species . The whole process can be expressed as reactions and Due to the irreversibility of the conversion reaction, the two cathode peaks in the first cycle vanished while two new peaks appeared around 1.9 and 1.2 V from the second cycle onward, which suggests the possible presence of a multistep Li + insertion mechanism . In the negative sweep, an inconspicuous anodic peak around ∼1.8 V appeared due to the incomplete oxidation of Mo metal to MoS 2 , and the other obvious peak around ∼2.4 V may be related to the oxidation of Li 2 S (Mo + 2Li 2 S ↔ Mo + 2S + 4Li) .…”

“…Due to the irreversibility of the conversion reaction, the two cathode peaks in the first cycle vanished while two new peaks appeared around 1.9 and 1.2 V from the second cycle onward, which suggests the possible presence of a multistep Li + insertion mechanism. 37 In the negative sweep, an inconspicuous anodic peak around ∼1.8 V appeared due to the incomplete oxidation of Mo metal to MoS 2 , and the other obvious peak around ∼2.4 V may be related to the oxidation of Li 2 S (Mo + 2Li 2 S ↔ Mo + 2S + 4Li). 38 In subsequent cycles, the anode peaks around 1.8 and 2.4 V are almost unchanged.…”