High-Performance Li-S Batteries with a Minimum Shuttle Effect: Disproportionation of Dissolved Polysulfide to Elemental Sulfur Catalyzed by a Bifunctional Carbon Host

Nitrogen-Doped Two-Dimensional Carbon Nanosheets for High-Sulfur-Loading Lithium-Sulfur Batteries via a Lignin-Based High-Internal-Phase Pickering Emulsion Strategy

Attributable to sulfur's significant theoretical energy density, its affordability, and its environmentally friendly nature, lithium-sulfur batteries (LSBs) are recognized as advanced energy storage technologies with considerable potential. Nonetheless, the solubility and migration of polysulfides within the electrolyte substantially hinder their practical implementation. To address this issue, we developed a nitrogen-doped two-dimensional (2D) wavy carbon nanosheet material (NCN) by using the Pickering emulsion templating method. Nitrogen doping enhances the surface polarity of the two-dimensional carbon material, promoting electrolyte penetration and providing strong chemical adsorption of polysulfides. The distinctive two-dimensional wavy structure enhances lithium-ion transport and regulates polysulfide dissolution and diffusion throughout the electrochemical cycle, resulting in an enhanced electrochemical performance. Therefore, the S@NCN cathode shows a discharge specific capacity, reaching 936 mAh g-1 at 1 C. Despite a sulfur load reaching 7.2 mg cm-2, the S@NCN cathode achieves a specific capacity of 823 mAh g-1. These findings indicate that the NCN is a high-performance 2D carbon material for sulfur cathodes, effectively improving the electrochemical stability of LSBs and showing great potential for future applications as a cathode material in LSBs.

Hydrogen-bonded micelle assembly directed conjugated microporous polymers for nanospherical carbon frameworks towards dual-ion capacitors

Well-orchestrated carbon nanostructure with superb stable framework and high surface accessibility is crucial for zinc-ion hybrid capacitors (ZIHCs). Herein, a hydrogen-bonded micelle self-assembly strategy is proposed for morphology-controllable synthesis of conjugated microporous polymers (CMPs) derived carbon to boost zinc ion storage capability. In the strategy, F127 micellar assembly through intermolecular hydrogen bonds serves as structure-directed agents, directing CMPs' oligomers grow into nanospherical assembly. The nanospherical carbon frameworks derived from CMPs (CNS-2) have shown maximized surface accessibility due to their plentiful tunable porosity and hierarchical porous structure with abundant mesoporous interconnected channels, and superb stability originating from CMPs' robust framework, thus the CNS-2-based ZIHCs exhibit ultrahigh energy density of 163 Wh kg-1 and ultralong lifespan with 93 % capacity retention after 200, 000 cycles at 20 A g-1. Charged ion storage efficiency also lies in dual-ion alternate uptake of Zn2+ and CF3SO3- as well as chemical redox of Zn2+ with carbonyl/pyridine motifs forming O-Zn-N bonds. Maximized surface accessibility and dual-ion storage mechanism ensure excellent electrochemical performance. Thus, the hydrogen-bond-guide micelle self-assembly strategy has provided a facile way to design nanoarchitectures of CMPs derived carbon for advanced cathodes of ZIHCs.

Demineralization of a Carbon Material Derived from Palm Kernel Shells as a Process for the Enhancement of the Electrochemical Performance of Lithium-Sulfur Cells

Carbon materials derived from biomass have been widely used in Li-S batteries; however, the mineral matter present in the biomass could impact the properties of the carbons and affect the electrochemical performance. In this study, the removal of mineral matter from palm kernel shells is reported to identify the effect of minerals on the physicochemical properties of the derived activated carbon and correlate them to the electrochemical performance in Li-S batteries. The content of minerals such as silicon, iron, and potassium was decreased by acid washing. The textural and conductive properties of activated carbon were increased by the absence of minerals. Electrochemical results reveal that the demineralized sample used as a sulfur host can increase the capacity for high charge and discharge rates by 23%. Hence, the removal of mineral matter in the biomass is an important step to consider for the application of activated carbons as sulfur hosts in Li-S batteries.

Multifunctional Lithium Phytate/Carbon Nanotube Double-Layer-Modified Separators for High-Performance Lithium-Sulfur Batteries

Li dendrite and the shuttle effect are the two primary hindrances to the commercial application of lithium-sulfur batteries (LSBs). Here, a multifunctional separator has been fabricated via successively coating carbon nanotubes (CNTs) and lithium phytate (LP) onto a commercial polypropylene (PP) separator to improve the performance of LSBs. The LP coating layer with abundant electronegative phosphate group as permselective ion sieve not only reduces the polysulfide shuttle but also facilitates uniform Li+ flux through the PP separator. And the highly conductive CNTs on the second layer act as a second collector to accelerate the reversible conversion of sulfide species. The synergistic effect of LP and CNTs further increases the electrolyte wettability and reaction kinetics of cells with a modified separator and suppresses the shuttle effect and growth of Li dendrite. Consequently, the LSBs present much enhanced rate performance and cyclic performance. It is expected that this study may generate an executable tactic for interface engineering of separator to accelerate the industrial application process of LSBs.

Chemical Interactions between Dissolved Polysulfides and Potential Catalytic Host Materials for Li-S Batteries

Given that both elemental sulfur (S8) and lithium sulfide (Li2S) exhibit insulating properties, the involvement of conductive host materials becomes crucial for facilitating charge transfer in sulfur cathodes within lithium-sulfur (Li-S) batteries. Furthermore, there has been a recent surge in the exploration of host materials for sulfur cathodes to address the "polysulfide shuttle" effect. This effect arises from the formation of polysulfide species during the charge-discharge cycles of the Li-S batteries and can be mitigated through physical or chemical interactions with specific materials. To qualitatively and accurately assess the interactions between polysulfides and the potential host materials, this study utilized a well-established high-performance liquid chromatography method for polysulfide analysis. The objective was to monitor the changes in polysulfide solutions after contact with 44 different carbon and inorganic materials. Based on both qualitative and quantitative chromatographic results, it was determined that 20 out of the 44 materials exhibit significant interactions with polysulfides. The primary form of interaction observed is the irreversible disproportionation reaction with elemental sulfur being one of the resulting products.