Rational construction of a CNTs@VO2 nanosheets modified separator for enhancing the performance of lithium-sulfur batteries.

Although lithium-sulfur (Li-S) batteries possess great potential to become the next generation of energy storage technology due to their fivefold higher energy density than commercial lithium-ion batteries, their practical application is still hindered by their poor cycling stability, especially resulting from the disturbing shuttle effect of soluble intermediates. In this study, vanadium dioxide (VO2) nanosheets were successfully grown onto CNTs to form CNTs@VO2 through hydrothermal and calcining processes. The hollow structure of the high conductive CNTs offers internal space and mesopores to accommodate the electrolyte combined with the polar metal oxide VO2 nanosheets providing the chemical anchoring. The hollow binary core-shell host acting as the nanoreactor that serves as the modifier of the separator results in the intensive physical and chemical dual adsorption of lithium polysulfide species (LiPSs), promoting the conversion of long-chain LiPSs to alleviate the shuttle effect significantly and boosting the performance. In addition, the CNTs enhance the electronic conductivity and the electrolyte infiltration of the separator. Notably, the modified separator demonstrates a high initial discharge capacity of 1397 mA h g-1 at 0.2C and retains a stable cycling ability with a reversible capacity of 965 mA h g-1 over 200 cycles at 1C. Even for the high sulfur loading of 7.4 mg cm-2, it can deliver a high areal capacity of 5.4 mA h cm-2 at 0.5C.

CoFe Alloy-Decorated Interlayer with a Synergistic Catalytic Effect Improves the Electrochemical Kinetics of Polysulfide Conversion.

Good electrical conductivity, strong catalytic activity, high interaction with lithium polysulfides (LIPSs), simple method, and low cost should be considered for the design and preparation of high-performance electrochemical catalysts that catalyze the conversion of LIPSs. In this work, we designed a bimetallic alloyed multifunctional interlayer with multiple adsorption/catalysis sites. The interwoven carbon fibers derived from bacterial cellulose (BC) not only contribute to reducing metal ions to metals but also confine the growth of Co-Fe alloys formed in situ. The metal supported on carbon is very effective for the conversion of LIPSs due to its high adsorption and catalytic sites. In addition, the synergistic effect between Fe and Co species leads to excellent bifunctional catalytic activity. Through detailed electrochemical analysis and theoretical calculations, we revealed that CoFe@CNFs has superior electrocatalytic activity, and the lithium-sulfur (Li-S) batteries with a catalytic interlayer can deliver satisfactory rate and cycle performance. At a high current density of 2C, the discharge capacity can still reach 627 mAh g-1. At a current density of 1C, the Coulombic efficiency is maintained at a level close to 100% during the whole cycle process and a satisfying low capacity decay of 0.08% per cycle. More importantly, even if the ambient temperature drops to 0 °C, the Li-S battery using the interlayer can still be charged and discharged normally and shows acceptable discharge capacity, which shows that it has good rate kinetics.

Mo2C Electrocatalysts for Kinetically Boosting Polysulfide Conversion in Quasi-Solid-State Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) suffer from sluggish reaction kinetics of sulfur-containing species and loss of soluble polysulfides (PSs) during cycling, especially in the case of liquid electrolytes. Here, we improve the kinetics of sulfur species by decorating Mo2C nanoparticles on carbon nanotubes (CNTs) as the host for sulfur active mass. In addition, by use of gel polymer electrolytes (GPEs) derived from in situ polymerization of 1,3-dioxolane (DOL) to mitigate the diffusion of PSs and improve the stability of Li stripping/plating. As a result, the sulfur cathodes are endowed with enhanced initial specific capacity and suppressed dissolution of sulfur species. The cells with CNT/Mo2C/S cathodes and GPE exhibit excellent electrochemical performance. The anodes cycled with GPE show remarkably enhanced lithium plating-stripping behavior. Benefitting from the synergistic effect, LSBs with higher energy density and improved durability are obtained, demonstrating a new approach for developing high-performance quasi-solid-state Li metal batteries.

Preparation and Insights of Smart Foams with Phototunable Foamability Based on Azobenzene-Containing Surfactants.

Smart foams with tunable foamability exhibit superb applications in many fields such as colloidal and interface science. Herein, we have synthesized an azobenzene-containing surfactant with excellent photoresponsiveness by a simple thiol-maleimide click reaction between thioglycolic acid and 4-(N-maleimide) azobenzene (MAB). The structure and the photoresponsive behavior of the novel surfactant are characterized. Depending on the solution concentration, the synthesized surfactant demonstrated various speeds for the trans/cis photoisomerization varying from 9 to 24 s for the given concentration range and excellent reversible photoisomerization cycling stability (more than 20 cycles) upon light irradiation. Based on these conformational switches, a series of phototriggered obvious surface properties (e.g., critical micelle concentration (CMC), surface tension (γ), and surface excess concentration (Γ)) changes of the surfactant are achieved. More specifically, the smart foam system with tunable foamability is realized. As-formed smart foams with rapid photocontrolled reversible foaming/defoaming transition and excellent cycling stability make them very attractive candidates for applications in wastewater treatment, green textile, oil extraction, and emulsification.