Three-dimensional macroporous graphene monoliths with entrapped MoS2nanoflakes from single-step synthesis for high-performance sodium-ion batteries

Hollow Carbon and MXene Dual-Reinforced MoS2 with Enlarged Interlayers for High-Rate and High-Capacity Sodium Storage Systems

Sodium-ion batteries (SIBs) and sodium-ion capacitors (SICs) are promising candidates for cost-effective and large-scale energy storage devices. However, sluggish kinetics and low capacity of traditional anode materials inhibit their practical applications. Herein, a novel design featuring a layer-expanded MoS2 is presented that dual-reinforced by hollow N, P-codoped carbon as the inner supporter and surface groups abundant MXene as the outer supporter, resulting in a cross-linked robust composite (NPC@MoS2 /MXene). The hollow N, P-codoped carbon effectively prevents agglomeration of MoS2 layers and facilitates shorter distances between the electrolyte and electrode. The conductive MXene outer surface envelops the NPC@MoS2 units inside, creating interconnected channels that enable efficient charge transfer and diffusion, ensuring rapid kinetics and enhanced electrode utilization. It exhibits a high reversible capacity of 453 mAh g-1 , remarkable cycling stability, and exceptional rate capability with 54% capacity retention when the current density increases from 100 to 5000 mA g-1 toward SIBs. The kinetic mechanism studies reveal that the NPC@MoS2 /MXene demonstrates a pseudocapacitance dominated hybrid sodiation/desodiation process. Coupled with active carbon (AC), the NPC@MoS2 /MXene//AC SICs achieve both high energy density of 136 Wh kg-1 at 254 W kg-1 and high-power density of 5940 W kg-1 at 27 Wh g-1 , maintaining excellent stability.

SnS nanosheets firmly bound in alkali-treated wrinkled MXene framework with enhanced lithium-ion storage

An alkali-treated MXene-SnS hybrid was prepared through hydrothermal methods. The Alk-MXene microplates provide highway for electronic transport, and the 3D wrinkled morphology ensures sufficient channels for Li⁺ diffusion. The alkali treatment of MXene gives Alk-MXene@SnS enhanced binding strength, which allows the SnS nanosheets to remain firm binding with the Alk-MXene substrate during cycling and overcome capacity decay caused by large volume change. The synergy between the two components guarantees the hybrid excellent electrochemical properties by enabling high electronic/ionic conductivity and superior kinetic properties as evidenced by EIS, GITT tests and DFT calculation. As a result, the Alk-MXene@SnS retains specific capacities of 519 mAh/g after 100 cycles at 200 mA g^-1, and 330 mAh/g at the high rate of 8000 mA g^-1. In addition, a reversible capacity of 421 mAh/g can be provided after long term cycle test at 1000 mA g^-1 for 800 cycles.

In-Situ growing tungsten Sulfide/Carbon nanosheets on sodium titanate nanorods to stabilize Surface-Structure for enhanced Sodium-ion storage

Sodium-ions hybrid capacitors (SIHCs) have been recognized as one of the most potential energy storage devices, which can deliver high power and energy densities simultaneously. However, the sluggish kinetics of electrode materials severely restricts the performance of SIHCs. Herein, N, P-codoped carbon and WS₂ nanosheets coating on sodium titanate nanorods (NTO@WS₂/N, PC) were first designed by in-situ growing process and sulfuration treatment for boosting sodium-ion storage. Specifically, NTO@WS₂/N, PC electrodes displayed a satisfactory specific capacity of 274.7 mAh g^-1 at 3.0 A g^-1 after 1200 cycles. Furthermore, as-assembled SIHCs delivered high-energy density of 112.1 Wh kg^-1 and high-power density of 4334.4 W kg^-1. Besides, long-term cycling test revealed that a remarkable capacity retention rate of 89.7% was obtained at 8.0 A g^-1 after 2000 cycles. The excellent cycling stability and rate property could be ascribed to following aspects. On the one hand, N, P-codoped carbon could enhance the electrical conductivity and strengthen the structural integrality of the composites. On the other hand, ultrathin WS₂ nanosheets and one-dimensional (1D) NTO nanorods structure were conducive to the rapid diffusion of Na⁺. This work provides a convenient technique to stabilize the structure of electrode materials, which can promote the practical application of SIHCs.

3D hollow cage copper cobalt sulfide derived from metal–organic frameworks for high-performance asymmetric supercapacitors

The fabrication of the advanced MOF-based 3D hollow cage ternary bimetallic material CuCo2S4 for high performance asymmetric supercapacitors.

Ab initio insights into the stabilization and binding mechanisms of MoS2 nanoflakes supported on graphene

An atomistic understanding of transition-metal dichalcogenide (TMD) nanoflakes supported on graphene (Gr) plays an important role in the tuning of the physicochemical properties of two-dimensional (2D) materials; however, our current atom-level understanding of 2D-TMD nanoflakes on Gr is far from satisfactory. Thus, we report a density functional theory investigation into the stabilization and binding mechanisms of (MoS2)n/Gr, where n = 1, 4, 6, 9, 12 and 16. We found an evolution of the (MoS2)n…Gr interactions from covalent and hybridization contributions for smaller nanoflakes (n = 1, 4) to vdW interactions for larger (MoS2)n nanoflakes (n ≥ 6); however, the coupling of the (MoS2)n and Gr electronic states for n = 1 and 4 is not intense enough to change the Dirac cones at the Gr monolayer. On average, the 1T'- and 2H-(MoS2)n nanoflakes bind with similar adsorption/interaction energies with Gr, and hence the (MoS2)n…Gr interactions do not change the high energetic preference of the 1T'- structures, which can be explained by the stabilizing role of the S-terminated edges in the 1T'-(MoS2)n in contrast with the destabilizing role of the edges in the 2H-(MoS2)n nanoflakes.

SnS Nanosheets Confined Growth by S and N Codoped Graphene with Enhanced Pseudocapacitance for Sodium-Ion Capacitors

Layered tin monosulfide (SnS) is a promising anode material for sodium-ion batteries because of its high theoretical capacity of 1020 mA h g^-1. Its large interlayer spacing permits fast sodium-ion transport, making it a viable candidate for sodium-ion capacitors (SICs). In this work, we designed and synthesized oriented SnS nanosheets confined in graphene in the presence of poly(diallyl dimethyl ammonium chloride) by electrostatic self-assembly during hydrothermal growth. SnS nanosheets growing along (l00) and (0l0) directions are suppressed because of the confinement by graphene, which exhibit smaller thickness and particle size. These nanostructures expose abundant open edges because of the presence of Sn⁴⁺-O, which offers rich active sites and Na⁺ easy transport pathways. Vacancies formed at these edges along with S and N codopants in the graphitic structure synergistically promoted Na⁺ surface adsorption/desorption. Such nanocomposites with SnS nanosheets confined by N,S codoped graphene demonstrated significantly enhanced pseudocapacitance. The SICs delivered excellent energy densities of 113 and 54 W h kg^-1 at power densities of 101 and 11 100 W kg^-1, respectively, with 76% capacity retention after 2000 cycles at 1 A g^-1.

Synthesis and electrochemical sodium-storage of few-layered MoS2/nitrogen, phosphorus-codoped graphene

Few-layered molybdenum disulfide/nitrogen, phosphorus co-doped graphene composites are synthesized by a quaternary phosphonium salt-assisted hydrothermal and annealing procedure. The prepared composites are analyzed by x-ray powder diffraction, x-ray photoelectron spectra, scanning electronic microscopy, transmission electronic microscopy, Raman spectra and nitrogen adsorption and desorption. Experimental results indicate that the MoS₂ nanosheets are of few-layered and defective structures and are well anchored on flexible conductive nitrogen, phosphorus co-doped graphene to constitute mesoporous composites with increased surface areas. Benefiting from the structural merits as well as surface-dominated pseudocapacitive contribution, the composite electrode presents a high electrochemical sodium storage capacity that arrives at 542 mAh g^-1 at a current density of 100 mA g^-1 with an excellent cyclability. Moreover, a superior high-rate capability can also be achieved.