Nanoscale CuFe 2 O 4 Uniformly Decorated on Nitrogen‐Doped Carbon Nanofibers as Highly Efficient Catalysts for Polysulfide Conversion in Lithium‐Sulfur Batteries

Application of Y-MOF-CNT-Derived Y2O3-C@CNT Composites in Lithium-Sulfur Battery Separators

In order to mitigate the shuttle effect of lithium polysulfides in lithium-sulfur batteries, we propose a yttrium-metal-organic framework-carbon nanotube (Y-MOF-CNT)-derived Y2O3-C@CNT composite for modifying the separator in this study. The Y-MOFs, comprising yttrium (Y) rare earth metal and terephthalic acid, exemplify a prototypical category of metal-organic framework (MOF) materials. They manifest the advantageous attributes associated with MOFs while concurrently possessing distinctive catalytic traits ascribed to rare earth elements. In this study, Y-MOF nanoparticles were synthesized on carbon nanotube (CNT) substrates via a facile aqueous solution method, succeeded by high-temperature carbonization to yield Y2O3-C@CNT composite materials. These composites were subsequently employed as coatings on one side of polyethylene (PE) separators. The resultant Y2O3-C@CNT composite inherits the particle-like morphology and porosity from its precursor Y-MOF, alongside the inherent conductivity in carbon-based materials. This amalgamation is conducive to polysulfide capture and catalytic conversion processes within lithium-sulfur batteries. The application of the Y2O3-C@CNT-coated PE separator effectively mitigated polysulfide shuttle effects and significantly enhanced the battery electrochemical performance. At a sulfur loading level of 3 mg cm-2 under a 0.5 C rate, an initial discharge specific capacity of 900 mAh g-1 was achieved. After 400 cycles, the discharge specific capacity remained at 483.85 mAh g-1 with a capacity retention rate of 53.7%. Upon increasing sulfur loading to 5 mg cm-2, the discharge specific capacity at a lower rate (0.1 C) reached 817.8 mAh g-1; even after 100 cycles, it maintained a value of 700 mAh g-1 with a capacity retention rate of 85.6%. Notably, our modified Y2O3-C@CNT separator demonstrated exceptional cycling stability, even under conditions involving high sulfur loading.

Hybrid Membrane Composed of Nickel Diselenide Nanosheets with Carbon Nanotubes for Catalytic Conversion of Polysulfides in Lithium-Sulfur Batteries

Lithium-sulfur batteries demonstrate enormous energy density are promising forms of energy storage. Unfortunately, the slow redox kinetics and polysulfides shuttle effect are some of the factors that prevent the its development. To address these issues, the hybrid membrane with combination of nickel diselenide nanosheets modified carbon nanotubes (NSN@CNTs) and utilized Li2 S6 catholyte for lithium sulfur battery. The conductive CNTs facilitates fast electronic/ionic transport, while the polarity of NSN as a strong affinity to lithium polysulfides, effectively anchoring them, facilitating the redox conversion of polysulfide species, and effectively diminishing reaction barriers. The cell with NSN@CNTs delivers the first discharge capacity of 1123.8 mAh g-1 and maintains 786.5 mAh g-1 after 300 cycles (0.2 C) at the sulfur loading 5.4 mg. Its rate capability is commendable, enabling it to sustain a capacity of 559.8 mAh g-1 even at a high discharge rate of 2 C. In addition, its initial discharge capacity can remain 8.33 mAh even at 10.8 mg for duration of 100 cycles. This research indicates the potential application of NSN@CNTs hybrid materials in lithium-sulfur batteries.

Design of a sulfur host with CuCo2O4 supported on carbon cloth for lithium sulfur batteries

A high-efficiency sulfur host with bimetallic oxide CuCo2O4 cubes supported on carbon cloth has been designed and used in lithium sulfur batteries, which can suppress the "shuttle effect" and boost the redox reaction kinetics. The unique three-dimensional cube-based structure realized a high sulfur loading of 7.1 mg cm-2, and the corresponding assembled lithium sulfur battery delivered excellent cycling stability over 100 cycles at 0.1C.

Identifying the Role of the Cationic Geometric Configuration in Spinel Catalysts for Polysulfide Conversion in Sodium-Sulfur Batteries

An AB2X4 spinel structure, with tetrahedral A and octahedral B sites, is a paradigmatic class of catalysts with several possible geometric configurations and numerous applications, including polysulfide conversion in metal-sulfur batteries. Nonetheless, the influence of the geometric configuration and composition on the mechanisms of catalysis and the precise manner in which spinel catalysts facilitate the conversion of polysulfides remain unknown. To enable controlled exposure of single active configurations, herein, Cotd2+ and Cooh3+ in Co3O4 catalysts for sodium polysulfide conversion are in large part replaced by Fetd2+ and Feoh3+, respectively, generating FeCo2O4 and CoFe2O4. Through an examination of electrochemical activation energies, the characterization of symmetric cells, and theoretical calculations, we determine that Cooh3+ serves as the active site for the breaking of S-S bonds, while Cotd2+ functions as the active site for the formation of S-Na bonds. The current study underlines the subtle relationship between activity and geometric configurations of spinel catalysts, providing unique insights for the rational development of improved catalysts by optimizing their atomic geometric configuration.