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.

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.

In-situ self-assembled hollow urchins F-Co-MOF on rGO as advanced anodes for lithium-ion and sodium-ion batteries.

To obtain MOFs materials with good electrochemical performance in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), a kind of hollow urchins Co-MOF with doping fluorine (F) was in-situ assembled on reduced graphene oxide (rGO) using a simple solvothermal reaction. According to XRD, XPS and EDS mapping analysis, the molecular structure should be Co2[Fx(OH)1-x]2(C8O4H4) (denoted as F-Co-MOF). When the composite material is used as active material to assemble LIBs, it not only presents the outstanding reversible capacity (1202.0 mA h g-1 at 0.1 A g-1), but also gives the excellent rate performance and cycle performance (771.5 mA h g-1 at 2 A g-1 after 550 repeated cycles). The remarkable lithium storage capacity of F-Co-MOF/rGO is also reflected in the full cell, where it can still maintain a high capacity of 165.2 mA h g-1 after 300 cycles at 0.2 A g-1. It benefits from the synergistic effect of F-Co-MOF and high conductive rGO networks, so that the reversibility of lithium and sodium storage can be improved. This kind of F doped solvothermal synthesis of MOFs is of great significance for the exploration of high performance materials.