Constructing three-dimensional ordered porous MoS2/C hierarchies for excellent high-rate long-life pseudocapacitive sodium storage

Porous graphene-like MoS2/carbon hierarchies for high-performance pseudocapacitive sodium storage

“…Note that the stacking S–Mo–S planes with more than 40 layers suggest the preferential crystal growth along the (002) direction, while too many stacking layers would hinder the fast Na + insertion/extraction processes. 17…”

“…2f shows the HRTEM image of MoS 2 /C100, revealing that only a few layers of MoS 2 can be detected, and the d spacing of (002) planes is enlarged to 1.1 nm, which can be owing to the incorporation of carbon species. 17 Moreover, the disordered thin MoS 2 sheets (as depicted by the red broken lines) can provide more active sites for sodium storage. 21 To reveal the elemental distribution, the high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) image of MoS 2 /C100 with corresponding EDS maps are provided in Fig.…”

“…Among various candidate anodes for SIBs, two-dimensional (2D) layered transition metal dichalcogenides have been widely investigated due to their weak van der Waals interaction forces, thus facilitating the insertion/extraction of Na + . 3,16–20 In this regard, molybdenum ( iv ) sulfide (MoS 2 ) has gained much attention because of its high theoretical capacity (670 mA h g −1 ) as well as large van der Waals gap (0.62 nm) along S–Mo–S layers. 16,21–24 However, low conductivity and severe volume variation lead to poor rate performance as well as rapid capacity fading upon cycling, therefore hindering its practical application in high energy/power density storage devices.…”

“…6,35–38 These nano/microstructures can provide sufficient space for volume variation and electrolyte contact, thus shortening the ion diffusion path. 17,39,40 Although these solutions have achieved improved electrochemical performance, MoS 2 still suffers from restacking along S–Mo–S due to van der Waals forces, thus leading to easy aggregation and pulverization of the active material during cycling. 41 To overcome this, some studies suggest that the weak van der Waals force along the z -axis makes it possible to delaminate bulk MoS 2 into an expanded few-layer structure through mechanical exfoliation as well as heteroatom intercalation, thus exposing more MoS 2 active sites directly to the electrolyte and improving its intrinsic conductivity as well as diffusivity.…”

Tunable oxygen defect density and location for enhancement of energy storage

“…This implies that surface-exposed oxygen defects may be the active surface ion adsorption sites in surface charge storage. The increase in surface oxygen defects introduces excess electrons around the adjacent Ti atom to ease the adsorption of sodium ions on the TiO 2 lattice surface due to the interaction of electrons and ions [46]. To evaluate the charge storage reversibility of all the N 2 -annealed SC electrodes, CV retention curves are shown in Fig.…”