Amongst the materials being investigated for supercapacitor electrodes, carbon based materials are most investigated. However, pure carbon materials suffer from inherent physical processes which limit the maximum specific energy and power that can be achieved in an energy storage device. Therefore, use of carbon-based composites with suitable nano-materials is attaining prominence. The synergistic effect between the pseudocapacitive nanomaterials (high specific energy) and carbon (high specific power) is expected to deliver the desired improvements. We report the fabrication of high capacitance asymmetric supercapacitor based on electrodes of composites of SnO2 and V2O5 with multiwall carbon nanotubes and neutral 0.5 M Li2SO4 aqueous electrolyte. The advantages of the fabricated asymmetric supercapacitors are compared with the results published in the literature. The widened operating voltage window is due to the higher over-potential of electrolyte decomposition and a large difference in the work functions of the used metal oxides. The charge balanced device returns the specific capacitance of ~198 F g−1 with corresponding specific energy of ~89 Wh kg−1 at 1 A g−1. The proposed composite systems have shown great potential in fabricating high performance supercapacitors.

Understanding redox mechanisms as well as interactions between redox species and electrolyte is critical for rational design of electrolyte/cathode systems for Li−S batteries. Here, we demonstrate in situ FT-IR with attenuated total reflection (ATR) to monitor both polysulfide (PS) speciation (S x 2− , 2 ≤ x ≤ 8) and triflate anion (electrolyte) coordination state while simultaneously discharging/charging a full battery coin cell. We report the concentration of various PS species as a function of voltage during cell discharge. In addition, we found that molecular-level changes occurred in the electrolyte salt anion in response to PS speciation. During discharge, PS dissolution increases total solute concentration, inducing anion interactions between low coordination state complexes ion pairs and free ionsto form aggregate complexes. Under fast cyclic voltammetry sweep, less progressive formation of all PSs, due to diffusion limitations, resulted in a higher concentration of aggregates and PSs even upon completion of discharge. This new application of in situ FT-IR offers direct insight into dynamic interactions between electrolyte salt and polysulfides fundamental in developing Li−S systems.

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We report the stabilization of titanium monoxide (TiO) nanoparticles in nanofibers through electrospinning and carbothermal processes and their unique bifunctionalityhigh conductivity and ability to bind polysulfidesin Li–S batteries. The developed three-dimensional TiO/carbon nanofiber (CNF) architecture with the inherent interfiber macropores of nanofiber mats provides a much higher surface area (∼427 m2 g–1) and overcomes the challenges associated with the use of highly dense powdered Ti-based suboxides/monoxide materials, thereby allowing for high active sulfur loading among other benefits. The developed TiO/CNF-S cathodes exhibit high initial discharge capacities of ∼1080, ∼975, and ∼791 mAh g–1 at 0.1, 0.2, and 0.5 C rates, respectively, with long-term cycling. Furthermore, freestanding TiO/CNF-S cathodes developed with rapid sulfur melt infiltration (∼5 s) eradicate the need of inactive elements, viz., binders, additional current collectors (Al-foil), and additives. Using postmortem X-ray photoelectron spectroscopy and Raman analysis, this study is the first to reveal the presence of strong Lewis acid–base interaction between TiO (3d2) and S x 2– through the coordinate covalent Ti–S bond formation. Our results highlight the importance of developing Ti-suboxides/monoxide-based nanofibrous conducting polar host materials for next-generation Li–S batteries.

This past decade has seen extensive research in lithium-sulfur batteries with exemplary works mitigating the notorious polysulfide shuttling. However, these works utilize ether electrolytes that are highly volatile severely hindering their practicality. Here, we stabilize a rare monoclinic γ-sulfur phase within carbon nanofibers that enables successful operation of Lithium-Sulfur (Li-S) batteries in carbonate electrolyte for 4000 cycles. Carbonates are known to adversely react with the intermediate polysulfides and shut down Li-S batteries in first discharge. Through electrochemical characterization and post-mortem spectroscopy/ microscopy studies on cycled cells, we demonstrate an altered redox mechanism in our cells that reversibly converts monoclinic sulfur to Li2S without the formation of intermediate polysulfides for the entire range of 4000 cycles. To the best of our knowledge, this is the first study to report the synthesis of stable γ-sulfur and its application in Li-S batteries. We hope that this striking discovery of solid-to-solid reaction will trigger new fundamental and applied research in carbonate electrolyte Li-S batteries.