ABSTRACT
The practical application of Li-S batteries is severely limited due to low sulfur utilization, sluggish sulfur redox kinetics, intermediate polysulfide dissolution/shuttling, and subsequent anode degradation. A smart cathode with efficient electrocatalyst and a protected anode is necessary. Herein, hollow carbon (HC) spheres are used as a sulfur host to improve the electrical conductivity and buffer the volume expansion of active materials. Considering the weak interaction between carbon and lithium polysulfides (LiPS), tungsten diboride (WB2 ) nanoparticles are used as a conductive additive. Both experimental and density functional theory (DFT) comprehensively exhibit that metallic WB2 nanoparticles can firmly anchor the LiPS through B-S bond formation, accelerate their electrocatalytic conversion, and immobilize them. DFT also reveals that boron interacts with LiPS either through molecular or dissociative adsorption depending on its boron layer arrangement in WB2 . Further, a freestanding lithiated-poly(4-styrene sulfonate) membrane constructed on lithium, offers a homogeneous Li-ion flux, stable interface, and protection from LiPS. Finally, cells with the HC-S+WB2 cathode and protected anode exhibit improved active material utilization, superior rate performance, and impressive cycling stability, even at high sulfur loading and less quantity of the electrolyte. Further, the pouch cells demonstrate high reversible capacity and an excellent capacity retention.
ABSTRACT
The development of sodium-ion batteries has been hindered so far by the large irreversible capacity of hard carbon anodes and other anode materials in the initial few cycles, as sodium ions coming from cathode materials is consumed in the formation of the solid-electrolyte interface (SEI) and irreversibly trapped in anodes. Herein, the successful synthesis of an environmentally benign and cost-effective sodium salt (Na2 C4 O4 ) is reported that could be applied as additive in cathodes to solve the irreversible-capacity issues of anodes in sodium-ion batteries. When added to Na3 (VO)2 (PO4 )2 F cathode, the cathode delivered a highly stable capacity of 135â mAh g-1 and stable cycling performance. The water-stable Na3 (VO)2 (PO4 )2 F cathode in combination with a water-soluble sacrificial salt eliminates the need for using any toxic solvents for laminate preparation, thus paving way for greener electrode fabrication techniques. A 100 % increase in capacity of sodium cells (full-cell configuration) has been observed when using the new sodium salt at a C-rate of 2C. Regardless of the electrode fabrication technique, this new salt finds use in both aqueous and non-aqueous cathode-fabrication techniques for sodium-ion batteries.
ABSTRACT
Three dimensional (3D) MoS2 nanoflowers are successfully synthesized by hydrothermal method. Further, a composite of as prepared MoS2 nanoflowers and rGO is constructed by simple ultrasonic exfoliation technique. The crystallography and morphological studies have been carried out by XRD, FE-SEM, TEM, HR-TEM and EDS etc. Here, XRD study revealed, a composite of exfoliated MoS2 with expanded spacing of (002) crystal plane and rGO can be prepared by simple 40 minute of ultrasonic treatment. While, FE-SEM and TEM studies depict, individual MoS2 nanoflowers with an average diameter of 200 nm are uniformly distributed throughout the rGO surface. When tested as sodium-ion batteries anode material by applying two different potential windows, the composite demonstrates a high reversible specific capacity of 575 mAhg(-1) at 100 mAg(-1) in between 0.01 V-2.6 V and 218 mAhg(-1) at 50 mAg(-1) when discharged in a potential range of 0.4 V-2.6 V. As per our concern, the results are one of the best obtained as compared to the earlier published one on MoS2 based SIB anode material and more importantly this material shows such an excellent reversible Na-storage capacity and good cycling stability without addition of any expensive additive stabilizer, like fluoroethylene carbonate (FEC), in comparison to those in current literature.
ABSTRACT
New Ru(ii)- and Os(ii)-polypyridyl complexes have been synthesized with pendant acetylacetone (acac) functionality for anchoring on nanoparticulate TiO2 surfaces with a goal of developing an alternate sensitizer that could be utilized for designing an efficient dye-sensitized solar cell (DSSC). Time-resolved transient absorption spectroscopic studies in the femtosecond time domain have been carried out. The charge recombination rates are observed to be very slow, compared with those for strongly coupled dye molecules having catechol as the anchoring functionality. The results of such studies reveal that electron-injection rates from the metal complex-based LUMO to the conduction band of TiO2 are faster than one would expect for an analogous complex in which the chromophoric core and the anchoring moiety are separated with multiple saturated C-C linkages. Such an observation is rationalized based on computational studies, and a relatively smaller spatial distance between the dye LUMO and the TiO2 surface accounted for this. Results of this study are compared with those for analogous complexes having a gem-dicarboxy group as the anchoring functionality for covalent binding to the TiO2 surface to compare the role of binding functionalities on electron-transfer dynamics.
