The role of selenium vacancies functionalized mediator of bimetal (Co, Fe) selenide for high-energy-density lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries are currently only in the basic research stage and have not been commercialized, which is mainly affected by the poor conductivity of sulfur/lithium sulfide (S/Li2S), volume expansion effect of sulfur and the shuttle effect of lithium polysulfides (LiPSs). Herein, a three dimensional (3D) carbon nanotubes (CNTs) decorated cubic Co9Se8-x/FeSe2-y (0 ï¼œ x ï¼œ 8, 0 ï¼œ y ï¼œ 2) composite (Co9Se8-x/FeSe2-y@CNTs) is developed, and used as the functionalized mediator on polypropylene (PP) in Li-S batteries. Benefiting from the good electrical conductivity, large number of Se vacancies and the triple block/adsorption/catalytic effects of Co9Se8-x/FeSe2-y@CNTs, the cell with Co9Se8-x/FeSe2-y@CNTs//PP modified separator delivers a high reversible capacity (1103.5 mA h g-1) at 1C after three cycles activation at 0.5C and remains 446 mA g h-1 after 750 cycles with a 0.08% capacity decay rate each cycle. Moreover, at 0.2C, a high areal capacity of 3.63 mA h cm-2 after 100 cycles with a high sulfur loading of 4.1 mg cm-2 is obtained. The in-situ XRD tests revealing the transition path of α-S8 â†’ Li2S â†’ ß-S8 during the first charge-discharge process, then ß-S8 â†’ Li2S â†’ ß-S8 conversion reaction in the next cycles, and firstly determine the sulfur-selenide active intermediates (Se1.1S6.9) during cycles. The work provides a new insight into the development of bimetallic selenide composites by defect engineering with highly adsorptive and catalytic properties for Li-S batteries.

Novel hydrothermal synthesis of Mn-TaS3@rGO nanocomposite as a superior multifunctional mediator for advanced Li-S batteries.

Because of its high theoretical capacity and energy density, the lithium-sulfur (Li-S) battery is a desirable next-generation energy storage technology. However, the shuttle effect of lithium polysulfide and the slow sulfur reaction kinetics remain significant barriers to Li-S battery application. In this work, tantalum trisulfide (TaS3) and selective manganese-doped tantalum trisulfide (Mn-TaS3) nanocomposites on reduced graphene oxide surface were developed via a one-step hydrothermal method for the first time and introduced as a novel multifunctional mediator in the Li-S battery. The surface engineering of Mn-TaS3@rGO with abundant defects not only exhibits the strong adsorption performance on lithium polysulfides (LiPSs) but also demonstrates the remarkable electrocatalytic effect on both the LiPSs conversion reaction in symmetric cell and the Li2S nucleation/dissolution processes in potentiostatic experiments, which would substantially promote the electrochemical performance of LSB. The cell assembled with Mn-TaS3@rGO/PP modified separator could significantly improve the cell conductivity and effectively accelerate the redox conversion of active sulfur during the charging/discharging process, which delivers exceptional long-term cycling with 683 mA h g-1 retention capacity after the 1000th cycle at 0.3C under the sulfur loading of 2.7 mg cm-2. Even at the E/S ratio as low as 5.0 µL mg-1, the reversible specific capacity of 692 mA h g-1 can be offered at 0.2C over 300 cycles. This research indicates that the novel Mn-TaS3@rGO multifunctional mediator is successfully fabricated and applied in Li-S batteries with extraordinary electrochemical performances and gives a strategy to explore the construction of a modified functional separator.

Extraordinary electrochemical performance of lithium-sulfur battery with 2D ultrathin BiOBr/rGO sheet as an efficient sulfur host.

There are many challenges such as the shuttling effect of soluble lithium polysulfides species (LiPSs) and the slow solid-state conversion between Li2S4 and Li2S in the development process of lithium-sulfur battery (LSB), so it is vital how to design and fabricate sulfur hosts with strong adsorption and good electrocatalysis. In this work, BiOBr in-situ forms onto both sides of reduced graphene oxide (rGO) to obtain a novel ultrathin BiOBr/rGO sheet, then self-constructing a hydrogel cylinder in shape, via a one-step hydrothermal process. The BiOBr/rGO composite with sandwich structure not only shows the outstanding adsorption effect on LiPSs, resulting from a strong bonding interaction between BiOBr/rGO and Li2S6 demonstrated by XPS technique, but also exhibits the extraordinary electrocatalytic performance on both the LiPSs conversion reaction in cyclic voltammetry experiment of symmetric cell and the Li2S nucleation process in potentiostatic deposited experiment, which will significantly improve the electrochemical performance of LSB. The S@BiOBr/rGO electrodes deliver the superior capacity and long cyclic stability with 882.2 mA h g-1 at 0.5 C after 1000 cycles, as well as displays the excellent rate performance with 823.9, 692.6 and 554.2 mA h g-1 at 1 C, 3 C and 5 C, respectively, after 400 cycles. Even though the sulfur loading reaches 4.9 mg cm-1, the reversible specific capacity of 424.6 mA h g-1can be maintained at 0.5 C after 400 cycles. Based on the in-situ X-ray diffraction and in-situ Raman spectroscopy, it could be revealed that the initial discharge process of active sulfur on the BiOBr/rGO cathode is α-S8 â†’ Li2S8 â†’ Li2S6 â†’ Li2S3 â†’ Li2S2 â†’ Li2S, while the charging progress is the corresponding reverse reaction, but the final substance is ß-S8. This research not only shows that the two-dimensional ultrathin BiOBr/rGO hybrid is successfully developed in LSB with excellent electrochemical performances, but also provides a strategy for exploring the construction of sulfur host materials.

Manipulating the electrocatalytic activity of sulfur cathode via distinct cobalt sulfides as sulfur host materials in lithium-sulfur batteries.

For the better development of lithium-sulfur (Li-S) batteries, it is necessary to fabricate sulfur hosts with cheap, rapid sulfur reaction dynamic and inhibiting the shuttling effect of lithium polysulfides (LiPSs). Herein, four hollow cubic materials with two kinds of nitrogen-doped carbon derived from Prussian blue analogues (PBA) precursor, Co9S8/MnS/NC@NC-400, CoS2/MnS/NC@NC-500, CoS1.097/MnS/NC@NC-600 and CoS1.097/MnS/NC@NC-700, are reported when the vulcanization temperatures are regulated at 400 °C, 500 °C, 600 °C and 700 °C, respectively. Among them, Co9S8/MnS/NC@NC-400, CoS2/MnS/NC@NC-500 and CoS1.097/MnS/NC@NC-600 have the similar hollow cubic structure, which can physically confine the LiPSs's shuttle, however, the Co vacancies of CoS1.097 in the CoS1.097/MnS/NC@NC-600 can promote the rearrangement of surface electrons, which is beneficial to the diffusion of Li+/e-, improving the electrochemical reaction kinetics. As for the CoS1.097/MnS/NC@NC-700 with the same substance but almost collapsed structure, the CoS1.097/MnS/NC@NC-600 can accommodate the volume expansion of sulfur conversion. In the four sulfur-host materials, the CoS1.097/MnS/NC@NC-600 not only displays the outstanding adsorption ability on LiPSs, but also presents the best electrocatalytic activity in the Li2S potentiostatic deposition experiments and active sulfur reduction/oxidation conversion reactions, greatly promoting the electrochemical performances of Li-S batteries. The S@CoS1.097/MnS/NC@NC-600 cathode can deliver 1010.2 mA h g-1 at 0.5 C and maintain 651.1 mA h g-1 after 200 cycles. In addition, the in-situ X-ray diffraction (in-situ XRD) test reveals that the sulfur conversion mechanism is the processes of the α-S8 â†’ Li2S â†’ ß-S8 (first cycle), then ß-S8 â†” Li2S during the subsequent cycles. Based on the fundamental understanding of the design and preparation of CoxSy/MnS/NC@NC hosts with the desired adsorption and catalysis functions, the work can provide new insights and reveal the defect-engineering to develop the advanced Li-S batteries.

Rod-like Ni0.5Co0.5C2O4·2H2O in-situ formed on rGO by an interface induced engineering: Extraordinary rate and cycle performance as an anode in lithium-ion and sodium-ion half/full cells.

Transition metal oxalates have attracted wide attention due to the characteristics of the conversion reaction as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), However, there are huge volume expansion and sluggish circulation dynamics during the reversible Li+ and Na+ insertion/extraction process, which would lead to unsatisfactory reversible capacity and stability. In order to solve these problems, a rod-like structure Ni0.5Co0.5C2O4·2H2O is in-situ formed on the reduced graphene oxide layer (Ni0.5Co0.5C2O4·2H2O/rGO) in a glycol-water mixture medium via an interface induced engineering strategy. Benefitting from the synergistic cooperation of nano-diameter rod-like structure and high conductive rGO networks, the experimental results show that the prepared Ni0.5Co0.5C2O4·2H2O/rGO electrode has predominant rate performance and ultra-long cycle stability. For the LIBs, it not only exhibits an ultrahigh reversible capacity (1179.9 mA h g-1 at 0.5 A g-1 after 300 cycles), but also presents outstanding rate and cycling performance (646.5 mA h g-1 at 5 A g-1 after 1200 cycles). Besides, the Ni0.5Co0.5C2O4·2H2O/rGO electrode displays remarkable sodium storage capacity of 221.6 mA h g-1 after 100 cycles at 0.5 A g-1. Further, the extraordinary electrochemical capability of Ni0.5Co0.5C2O4·2H2O/rGO active material is also reflected in two full-cells, assembled using commercial LiCoO2 as cathode for LIBs and commercial Na3V2(PO4)3 as cathode for SIBs, both of which can show wonderful specific capacity and cycling stability. It is found in in-situ Raman experiments that the reversible changes of oxalate peaks are monitored in a charge/discharge process, which is scientific evidence for the transform reaction mechanism of metal oxalates in LIBs. These findings not only provide important ideas for studying the charge/discharge storage mechanism but also give scientific basis for the design of high-performance electrode materials.

Enormous-sulfur-content cathode and excellent electrochemical performance of Li-S battery accouched by surface engineering of Ni-doped WS2@rGO nanohybrid as a modified separator.

The poor conductivity of sulfur, the lithium polysulfide's shuttle effect, and the lithium dendrite problem still impede the practical application of lithium-sulfur (Li-S) batteries. In this work, the ultrathin nickel-doped tungsten sulfide anchored on reduced graphene oxide (Ni-WS2@rGO) is developed as a new modified separator in the Li-S battery. The surface engineering of Ni-WS2@rGO could enhance the cell conductivity and afford abundant chemical anchoring sites for lithium polysulfides (LiPSs) adsorption, which is convinced by the high adsorption energy and the elongate SS bond given using density-functional theory (DFT) calculation. Concurrently, the Ni-WS2@rGO as a modified separator could effectively catalyze the conversion of LiPSs during the charging/discharging process. The Li-S cell with Ni-WS2@rGO modified separator achieves a high initial capacity of 1160.8 mA h g-1 at the current density of 0.2C with a high-sulfur-content cathode up to 80 wt%, and a retained capacity of 450.7 mA h g-1 over 500 cycles at 1C, showing an efficient preventing polysulfides shuttle to the anode while having no influence on Li+ ion transference across the decorating separator. The strategy adopted in this work would afford an effective pathway to construct an advanced functional separator for practical high-energy-density Li-S batteries.

Minimal TiO2 Coupled with Conductive Polymer-Stimulated Synergistic Effect on Fast and Reversible Sodium-Ion Storage for Bismuth Sulfide.

Designing multiphase composition is believed to availably boost the structural integrity and electrochemical properties of sodium-ion battery anodes. Herein, a conceive of nanoflowers, assembled with Bi2S3 nanorods, is demonstrated to construct the multiphase composition involving TiO2 coating and polypyrrole (PPy) encapsulation. Bi2S3 acted as the dominating active material, in consideration of the low content of TiO2, which ensured the high capacity of the composite. The dual-structural restrain of the TiO2 and PPy coatings can effectively alleviate volume variation based on the pseudo-"zero-strain" effect of TiO2 and high flexibility of PPy shells. Meanwhile, the heterointerface greatly enhanced the coupling effect between Bi2S3 and TiO2 and thus improved the electrochemical performance, which was proved by the results of density functional theory calculation and electrochemical tests. Combining the regulation from the Bi2S3/TiO2 heterojunction and the dual-structural restrain effect, the Bi2S3/TiO2@PPy electrode exhibited excellent rate performance and superior cycle stability (275.8 mA h g-1 over 500 cycles at 10 A g-1). This study indicates that designing multiphase composition can be very promising and provides a structural insight to construct high stability in electrodes for sodium-ion batteries.

Open and Closed Layered Nanostructures with Sub-10 nm Periodicity Self-Assembled from Hydrophilic [60]Fullerene-Based Giant Surfactants.

Giant surfactants have been identified as good candidates to produce sub-10 nm elaborate nanostructures, which could potentially realize complex functions in nanofabrication fields. Our theoretical simulation demonstrates the formation of open layered (pupa-like micelles) and closed layered (onion-like micelles) nanostructures, self-assembled from giant surfactants with comparably sized hydrophilic heads tethered by oligomers in solution. Directed by these simulation results, we synthesized giant surfactants consisting of hydrophilic [60]fullerene heads and oligostyrene (OS7) tails and produced the predicted nanostructures with periods of 9.5, 8.3, and 7.5 nm, experimentally. Adjusting the polarity of the solvent and corresponding concentration changed the nanostructures from onion-like micelles with closed layers to pupa-like micelles with open layers. The different morphologies and periods were caused by solvent inclusion and the overlap of OS chains. The above layered nanostructures remained stable after annealing at 120 °C. This work provides insights that computer simulation can play an important role in assisting the design and construction of complicated nanostructures in giant surfactant systems.

Novel magnetically separable anhydride-functionalized Fe3O4@SiO2@PEI-NTDA nanoparticles as effective adsorbents: synthesis, stability and recyclable adsorption performance for heavy metal ions.

In this paper, a novel adsorbent, Fe3O4@SiO2@PEI-NTDA, was first prepared by the immobilization of an amine and anhydride onto magnetic Fe3O4@SiO2 nanoparticles with polyethylenimine (PEI) and 1,4,5,8-naphthalenetetracarboxylic-dianhydride (NTDA) for the removal of heavy metal ions from aqueous solutions. The structure of Fe3O4@SiO2@PEI-NTDA was systematically investigated; the results confirmed that amine and anhydride groups were successfully covalently grafted onto the surface of Fe3O4@SiO2, which showed a homogenous core-shell structure with three layers of about 300 nm diameter (Fe3O4 core: 200 nm, nSiO2 layer: 20 nm, and PEI-NTDA layer: 20 nm). The adsorption performance of Fe3O4@SiO2@PEI-NTDA NPs was evaluated for single Pb2+ and coexisting Cd2+, Ni2+, Cu2+, and Zn2+ ions in an aqueous solution in a batch system. The amine and anhydride groups may have a synergistic effect on Pb2+ removal through electrostatic interactions and chelation; Fe3O4@SiO2@PEI-NTDA NPs exhibited preferable removal of Pb2+ with maximum adsorption capacity of 285.3 mg g-1 for Pb2+ at a solution pH of 6.0, adsorbent dosage of 0.5 g L-1, initial Pb2+ concentration of 200 mg L-1 and contact time of 3 h. The adsorption mechanism conformed well to the Langmuir isotherm model, and the adsorption kinetic data were found to fit the pseudo-second order model. Fe3O4@SiO2@PEI-NTDA NPs could be recovered easily from their dispersion by an external magnetic field and demonstrated good recyclability and reusability for at least 6 cycles with a high adsorption capacity above 204.5 mg g-1. The magnetic adsorbents showed high stability with a weight loss below 0.65% in the acid leaching treatment by 2 M HCl solution for 144 h. This study indicates that Fe3O4@SiO2@PEI-NTDA NPs are new promising adsorbents for the effective removal of Pb2+ in wastewater treatment.