Superhierarchical Conductive Framework Implanted with Nickel/Graphitic Carbon Nanocages as Sulfur/Lithium Metal Dual-Role Hosts for Li-S Batteries

Establishing Transition Metal Phosphides as Effective Sulfur Hosts in Lithium-Sulfur Batteries through the Triple Effect of "Confinement-Adsorption-Catalysis"

Structurally optimized transition metal phosphides are identified as a promising avenue for the commercialization of lithium-sulfur (Li-S) batteries. In this study, a CoP nanoparticle-doped hollow ordered mesoporous carbon sphere (CoP-OMCS) is developed as a S host with a "Confinement-Adsorption-Catalysis" triple effect for Li-S batteries. The Li-S batteries with CoP-OMCS/S cathode demonstrate excellent performance, delivering a discharge capacity of 1148 mAh g-1 at 0.5 C and good cycling stability with a low long-cycle capacity decay rate of 0.059% per cycle. Even at a high current density of 2 C after 200 cycles, a high specific discharge capacity of 524 mAh g-1 is maintained. Moreover, a reversible areal capacity of 6.56 mAh cm-2 is achieved after 100 cycles at 0.2 C, despite a high S loading of 6.8 mg cm-2 . Density functional theory (DFT) calculations show that CoP exhibits enhanced adsorption capacity for sulfur-containing substances. Additionally, the optimized electronic structure of CoP significantly reduces the energy barrier during the conversion of Li2 S4 (L) to Li2 S2 (S). In summary, this work provides a promising approach to optimize transition metal phosphide materials structurally and design cathodes for Li-S batteries.

Synergy between highly dispersed Ni nanocrystals and graphitized carbon derived from a single source as a strategy for high performance Lithium-Sulfur batteries

Due to their higher energy density, lower prices, and more environmentally friendly active components, Li-S batteries will soon compete with the current Li-ion batteries. However, issues persist that hinder this implementation, such as the poor conductivity of S and sluggish kinetics due to the polysulfide shuttle, among others. Herein, Ni nanocrystals encapsulated in a C matrix are obtained by a novel strategy based on the thermal decomposition of a Ni oleate-oleic acid complex at low-to-moderate temperatures: 500 and 700 °C. The two C/Ni composites were employed as hosts in Li-S batteries. Although the C matrix is amorphous at 500 °C, it is highly graphitized at 700 °C. At this moderate temperature, the simultaneous generation of Ni nanocrystals and the carbon matrix enhances the catalytic activity of Ni toward the graphitization process, which is negligible if starting from a mixture of a Ni salt and carbon source, even when calcined at temperatures as high as 1000 °C. The electrode made from the C/Ni composite obtained at 700 °C exhibits a high reversible capacity and an enhanced rate capability, much better not only than the C/Ni composite obtained at 500 °C but than others based on amorphous C calcined at very high temperatures, around 1000 °C. These properties are attributed to an increase in the electrical conductivity parallel to the ordering of the layers. We believe this work provides a new strategy to design C-based composites capable of combining the formation of nanocrystalline phases and the control of the C structure with superior electrochemical properties for Li-S batteries.

Ni-CeO2 Heterostructures in Li-S Batteries: A Balancing Act between Adsorption and Catalytic Conversion of Polysulfide

Lithium-sulfur (Li-S) batteries have attracted considerable attention over the last two decades because of a high energy density and low cost. However, the wide application of Li-S batteries has been severely impeded due to the poor electrical conductivity of S, shuttling effect of soluble lithium polysulfides (LiPSs), and sluggish redox kinetics of S species, especially under high S loading. To address all these issues, a Ni-CeO₂ heterostructure-doped carbon nanofiber (Ni-CeO₂ -CNF) is developed as an S host that combines the strong adsorption with the high catalytic activity and the good electrical conductivity, where the LiPSs anchored on the heterostructure surface can directly gain electrons from the current collector and realize a fast conversion between S₈ and Li₂ S. Therefore, Li-S batteries with S@Ni-CeO₂ -CNF cathodes exhibit superior long-term cycling stability, with a capacity decay of 0.046% per cycle over 1000 cycles, even at 2 C. Noteworthy, under a sulfur loading up to 6 mg cm^-2 , a high reversible areal capacity of 5.3 mAh cm^-2 can be achieved after 50 cycles at 0.1 C. The heterostructure-modified S cathode effectively reconciles the thermodynamic and kinetic characteristics of LiPSs for adsorption and conversion, furthering the development of high-performance Li-S batteries.

Structural and Surfacial Modification of Carbon Nanofoam as an Interlayer for Electrochemically Stable Lithium-Sulfur Cells

Electrochemical lithium-sulfur batteries engage the attention of researchers due to their high-capacity sulfur cathodes, which meet the increasing energy-density needs of next-generation energy-storage systems. We present here the design, modification, and investigation of a carbon nanofoam as the interlayer in a lithium-sulfur cell to enable its high-loading sulfur cathode to attain high electrochemical utilization, efficiency, and stability. The carbon-nanofoam interlayer features a porous and tortuous carbon network that accelerates the charge transfer while decelerating the polysulfide diffusion. The improved cell demonstrates a high electrochemical utilization of over 80% and an enhanced stability of 200 cycles. With such a high-performance cell configuration, we investigate how the battery chemistry is affected by an additional polysulfide-trapping MoS2 layer and an additional electron-transferring graphene layer on the interlayer. Our results confirm that the cell-configuration modification brings major benefits to the development of a high-loading sulfur cathode for excellent electrochemical performances. We further demonstrate a high-loading cathode with the carbon-nanofoam interlayer, which attains a high sulfur loading of 8 mg cm-2, an excellent areal capacity of 8.7 mAh cm-2, and a superior energy density of 18.7 mWh cm-2 at a low electrolyte-to-sulfur ratio of 10 µL mg-1.

Leather Solid Waste/Poly(vinyl alcohol)/Polyaniline Aerogel with Mechanical Robustness, Flame Retardancy, and Enhanced Electromagnetic Interference Shielding

Renewable biobased aerogels display a promising potential to fulfill the surging demand in various industrial sectors. However, its inherent low mechanical robustness, flammability, and lack of functionality are still huge obstacles in its practical application. Herein, a novel integrated leather solid waste (LSW)/poly(vinyl alcohol) (PVA)/polyaniline (PANI) aerogel with high mechanical robustness, flame retardancy, and electromagnetic interference (EMI) shielding performance was successfully prepared. Amino carboxyl groups in LSW could be effectively exposed by solid-state shear milling (S³ M) technology to form strong hydrogen-bond interactions with the PVA molecular chains. This led to a change in the compressive strength and the temperature of the initial dimensional change to 15.6 MPa and 112.7 °C at a thickness of 2.5 cm, respectively. Moreover, LSW contains a large number of N elements, which ensures a nitrogen-based flame-retardant mechanism and increase in the limit oxygen index value of LSW/PVA aerogel to 32.0% at a thickness of 2.5 mm. Notably, by the cyclic coating method, a conductive PANI layer could be polymerized on the surface of LSW/PVA aerogel, which led to the construction of a sandwich structure with impressive EMI shielding capability. The EMI shielding effectiveness (SE) reached more than 40 dB, and the specific shielding effectiveness (SSE) reached 73.0 dB cm³ g^-1. The inherent dipoles in collagen fibers and the conductive PANI synergistically produced an internal multiple reflection and absorption mechanism. The comprehensive performance of LSW/PVA/PANI aerogel not only demonstrates a new strategy to recycle LSW in a more value-added way but also sheds some more light on the development of biomass aerogels with high-performance, environmentally friendly, and cost-effective properties.