Transition Metal d-band Center Tuning by Interfacial Engineering to Accelerate Polysulfides Conversion for Robust Lithium-Sulfur Batteries.

Although lithium-sulfur batteries (LSBs) promise high theoretical energy density and potential cost effectiveness, their applications are severely impeded by the shuttling and sluggish redox kinetics of lithium polysulfides (LiPSs). In this context, a Co9 S8 @MoS2 heterostructure is sophisticatedly designed as an efficient catalytic host to boost the sulfur reduction reaction/evolution reaction (SRR/SER) kinetics and suppresses the LiPSs shuttling in LSBs. The results indicate that the electronic structure is manipulated in the Co9 S8 @MoS2 heterostructure, where the built-in electric fields (BIEFs) within the heterointerfaces enable the sufficient adsorption sites to accelerate the ionic diffusion/charge transfer kinetics for LiPSs redox, thus enhancing the sulfur conversion. By tuning the electronic structure, the metal d-band of Co9 S8 @MoS2 heterostructure plays an important role in adsorbing and catalyzing the conversion of LiPSs, thus promoting the reaction kinetics of the corresponding LSBs. This work unlocks the potential of heterostructures as promising catalysts to the design of high-energy and stabilized LSBs.

Sheet-Like Stacking SnS2/rGO Heterostructures as Ultrastable Anodes for Lithium-Ion Batteries.

SnS2-based materials have attracted considerable attention in energy storage and conversion owing to their high lithium activity and theoretical capacity. However, the practical application is severely limited by the low coulombic efficiency and short cycle life due to irreversible side reactions, low conductivity, and serious pulverization in the discharge/charge process. In this study, sheet-like stacking SnS2/reduced graphene oxide (rGO) heterostructures were developed using a facile solvothermal method. It was found that the composites between SnS2 nanoplates and rGO nanosheets are closely coupled through van der Waals interactions, providing efficient electron/ion paths to ensure high electrical conductivity and sufficient buffer space to alleviate volume expansion. Therefore, the SnS2/rGO heterostructure anode can obtain a high capacity of 840 mA h g-1 after 120 cycles at a current density of 200 mA g-1 and maintain a capacity of 450 mA h g-1 after 1000 cycles at 1000 mA g-1. In situ X-ray diffraction tests showed that SnS2/rGO undergoes typical initial intercalation, conversion, and subsequent alloying reactions during the first discharge, and most of the reactions are dealloying/alloying in the subsequent cycles. The galvanostatic intermittent titration technique showed that the diffusion of lithium ions in the SnS2/rGO heterostructures is faster in the intercalation and conversion reactions than in the alloying reactions. These observations help to clarify the reaction mechanism and ion diffusion behavior in the SnS2 anode materials, thus providing valuable insights for improving the energy efficiency of lithium-ion batteries.

Ion-Selective Covalent Organic Framework Membranes as a Catalytic Polysulfide Trap to Arrest the Redox Shuttle Effect in Lithium-Sulfur Batteries.

In the wake of shaping the energy future through materials innovation, lithium-sulfur batteries (LSBs) are top-of-the-line energy storage system attributed to their high theoretical energy density and specific capacity inclusive of low material costs. Despite their strengths, LSBs suffer from the cross-over of soluble polysulfide redox species to the anode, entailing fast capacity fading and inferior cycling stability. Adding to the concern, the insulating character of polysulfides lends to sluggish reaction kinetics. To address these challenges, we construct optimized polysulfide blockers-cum-conversion catalysts by accommodating the battery separator with covalent organic framework@Graphene (COF@G) composites. We settle on a crystalline TAPP-ETTB COF in the interest of its nitrogen-enriched scaffold with a regular pore geometry, providing ample lithiophilic sites for strong chemisorption and catalytic effect to polysulfides. On another front, graphene enables high electron mobility, boosting the sulfur redox kinetics. Consequently, a lithium-sulfur battery with a TAPP-ETTB COF@G-based separator demonstrates a high reversible capacity of 1489.8 mA h g-1 at 0.2 A g-1 after the first cycle and good cyclic performance (920 mA h g-1 after 400 cycles) together with excellent rate performance (827.7 mA h g-1 at 2 A g-1). The scope and opportunities to harness the designability and synthetic structural control in crystalline organic materials is a promising domain at the interface of sustainable materials, energy storage, and Li-S chemistry.

Sandwich-like SnS2/graphene multilayers for efficient lithium/sodium storage.

2D materials have attracted extensive attention in energy storage and conversion due to their excellent electrochemical performances. Herein, we report utilization of monolayer SnS2 sheets within SnS2/graphene multilayers for efficient lithium and sodium storage. SnS2/graphene multilayers are synthesized through a solution-phase direct assembly method by electrostatic interaction between monolayer SnS2 and PDDA (polydimethyl diallyl ammonium chloride)-graphene nanosheets. It has been shown that the SnS2/graphene multilayer electrode has a large pseudocapacity contribution for enhanced lithium and sodium storage. Typical batteries deliver a stable reversible capacity of ∼160 mA h g-1 at 2 A g-1 after 2000 cycles for lithium and a stable reversible capacity of ∼142 mA h g-1 at 1 A g-1 after 1000 cycles for sodium. The excellent electrochemical performances of SnS2/graphene multilayers are attributed to the synergistic effect between the monolayer SnS2 sheets and the PDDA-graphene nanosheets. The multilayer structure assembled by different monolayer nanosheets is promising for the further development of 2D materials for energy storage and conversion.

Cr-Doped Urchin-Like WO3 Hollow Spheres: The Cooperative Modulation of Crystal Growth and Energy-Band Structure for High-Sensitive Acetone Detection.

Acetone is a biomarker in the exhaled breath of diabetic patients; sensitive and selective detection of acetone in human exhaled breath plays an important role in noninvasive diagnosis. Tungsten oxide (especially for γ-WO3) is a promising material for the detection of breath acetone. It is generally believed that the stable metastable phase of WO3 (ε-WO3) is the main reason for the improved response to acetone detection. In this work, pure and Cr-doped urchin-like WO3 hollow spheres were synthesized by a facile hydrothermal approach. Analyses of the resulting materials via X-ray photoelectron spectroscopy (XPS) and Raman confirmed that they are mainly composed by γ-WO3. The gas sensing performances of pure and Cr-doped WO3 to acetone were systematically tested. Results show that the sensor based on pure WO3 annealed at 450 °C has a high response of 20.32 toward 100 ppm acetone at a working temperature of 250 °C. After doped with Cr, the response was increased 3.5 times higher than the pure WO3 sensor. The pure and Cr-doped WO3 sensors both exhibit a tiny response to other gases, low detection limits (ppb-level) and an excellent repeatability. The improvement of gas sensing properties could be attributed to an optimized morphology of Cr-doped WO3 by regulating the crystal growth and reducing the assembled nanowires' diameter. The increasing number of oxygen vacancy and the introduction of impurity energy level with trap effect after Cr doping would lead to the wider depletion layer as well as a better gas sensing performance. This work will contribute to the development of new WO3 acetone sensors with a novel morphology and will explain the increased response after Cr doping from a new perspective.

Nb2 O5 /RGO Nanocomposite Modified Separators with Robust Polysulfide Traps and Catalytic Centers for Boosting Performance of Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) have shown great potential for application in high-density energy storage systems. However, the performance of LSBs is hindered by the shuttle effect and sluggish reaction kinetics of lithium polysulfides (LiPSs). Herein, heterostructual Nb2 O5 nanocrystals/reduced graphene oxide (Nb2 O5 /RGO) composites are introduced into LSBs through separator modification for boosting the electrochemical performance. The Nb2 O5 /RGO heterostructures are designed as chemical trappers and conversion accelerators of LiPSs. Originating from the strong chemical interactions between Nb2 O5 and LiPSs as well as the superior catalytic nature of Nb2 O5 , the Nb2 O5 /RGO nanocomposite possesses high trapping efficiency and efficient electrocatalytic activity to long-chain LiPSs. The effective regulation of LiPSs conversion enables the LSBs enhanced redox kinetics and suppressed shuttle effect. Moreover, the Nb2 O5 /RGO nanocomposite has abundant sulfophilic sites and defective interfaces, which are beneficial for the nucleation and growth of Li2 S, as evidenced by analysis of the cycled separators. As a result, LSBs with the Nb2 O5 /RGO-modified separators exhibit excellent rate capability (816 mAh g-1 at 3 A g-1 ) and cyclic performance (628 mAh g-1 after 500 cycles). Remarkably, high specific capacity and stable cycling performance are demonstrated even at an elevated temperature of 50 °C or with higher sulfur loadings.