A Supramolecular Capsule for Reversible Polysulfide Storage/Delivery in Lithium-Sulfur Batteries

Fabrication of a Multi-Functional Separator Incorporating Crown ether- Polyoxometalate Supramolecular Compound for Lithium-Sulfur Batteries

Recently, research on polyoxometalates (POMs) has gained significant momentum. Owing to their properties as electronic sponges, POMs catalyst harbor substantial potential in lithium-sulfur battery research. However, POMs undergo a transformation into reduced heteropoly blue (HPB) during electrochemical reactions, which then dissolve into the electrolyte, resulting in catalyst loss. In this research, we amalgamated 18-crown-6 (CR6) with K3PW12O40, (KPW), synthesized a novel POM-based supramolecular compound, and integrated it with graphene oxide (GO) to fabricate a multi-functional composite polypropylene (PP) separator KPW-CR6/GO/PP. The crown ether array was employed to immobilize POM and construct ion transport channels, thereby enhancing the Li+ migration rate and capturing polysulfides. Subsequently, leveraging the stable structure and redox properties of POM, the polysulfide is catalyzed to transform and inhibit the shuttle effect, thereby protecting the Li anode. The lithium-sulfur batteries with the Crown ether-POM supramolecular compound separators, exhibit enhanced capacity and stability (1073.3 mAh g-1 at 1.0 C, and 81.5 % retention rate after 250 cycles). The battery (S loading: 3.2 mg cm-2) presents an initial specific discharge capacity of 543.4 mAh g-1 at 0.5 C, with 89.8 % of the capacity retained after 160 cycles. This underlines the practical application potential of Crown ether-POM supramolecular materials in Li-S batteries.

A Supramolecular Complex of C60 -S with High-Density Active Sites as a Cathode for Lithium-Sulfur Batteries

The well-known "shuttle effect" of the intermediate lithium polysulfides (LiPSs) and low sulfur utilization hinder the practical application of lithium-sulfur (Li-S) batteries. Herein, we describe a novel C₆₀ -S supramolecular complex with high-density active sites for LiPS adsorption that was formed by a simple one-step process as a cathode material for Li-S batteries. Benefiting from the cocrystal structure, 100 % of the C₆₀ molecules in the complex can offer active sites to adsorb LiPSs and catalyze their conversion. Furthermore, the lithiated C₆₀ cores promote internal ion transport inside the composite cathode. At a low electrolyte/sulfur ratio of 5 μL mg^-1 , the C₆₀ -S cathode with a sulfur loading of 4 mg cm^-2 exhibited a high capacity of 809 mAh g^-1 (3.2 mAh cm^-2 ). The development of the C₆₀ -S supramolecular complex will inspire the invention of a new family of S/fullerenes as cathodes for high-performance Li-S batteries and extend the application of fullerenes.

Synchronous Gains of Areal and Volumetric Capacities in Lithium-Sulfur Batteries Promised by Flower-like Porous Ti3C2T x Matrix

The areal and volumetric capacities are important metrics in practical deployment of advanced energy storage systems with the imposed constraints of device volume and chip area. Conductive carbons are promising sulfur host materials for improving areal capacity in lithium-sulfur (Li-S) batteries, but they face a few congenital deficiencies, such as low tap density and weak polysulfide entrapment ability, resulting in poor volumetric performance. Here, we report one type of cathode system based on flower-like porous Ti₃C₂T _x (FLPT) without the incorporation of any carbon hosts or conductive additives. The resultant FLPT-S electrode synchronously acquires a high areal capacity of 10.04 mAh cm^-2 and ultrahigh volumetric capacity of 2009 mAh cm^-3. Furthermore, ex situ electron paramagnetic resonance and UV-visible spectra have demonstrated that FLPT enables a fast dynamic equilibrium between S₆^2- anion and S₃^•- radical during cycling, which promotes the redox reactions of sulfur species.