Ordered Mesoporous Graphitic Carbon/Iron Carbide Composites with High Porosity as a Sulfur Host for Li-S Batteries

Dual-Functional Hosts for Polysulfides Conversion and Lithium Plating/Stripping towards Lithium-Sulfur Full Cells

The practical application of lithium-sulfur (Li-S) batteries is greatly hindered by the shuttle effect of dissolved polysulfides in the sulfur cathode and the severe dendritic growth in the lithium anode. Adopting one type of effective host with dual-functions including both inhibiting polysulfide dissolution and regulating Li plating/stripping, is recently an emerging research highlight in Li-S battery. This review focuses on such dual-functional hosts and systematically summarizes the recent research progress and application scenarios. Firstly, this review briefly describes the stubborn issues in Li-S battery operations and the sophisticated counter measurements over the challenges by dual-functional behaviors. Then, the latest advances on dual-functional hosts for both cathode and anode in Li-S full cells are catalogued as species, including metal chalcogenides, metal carbides, metal nitrides, heterostuctures, and the possible mechanisms during the process. Besides, we also outlined the theoretical calculation tools for the dual-functional host based on the first principles. Finally, several sound perspectives are also rationally proposed for fundamental research and practical development as guidelines.

FeCo/Fe3C-cross-linked N-doped carbon via synergistic confinement and efficient catalyst to enable high-performance Li-S batteries

Lithium-sulfur batteries (LSB) with high specific energy capacity and low material costs promise to be the next generation of energy storage devices. However, their commercialization is holding back by the poor cycling stability and fast capacity fading resulting from the shuttle effect and slow redox reaction. In this work, the FeCo/Fe₃C-CNC composite was prepared by anchoring FeCo/Fe₃C nanoparticles onto the crosslinked N-doped Carbon (CNC). The results showed that the addition of Co element improved the electrochemical activity of Co-Fe alloy through tuning the electronic structure of Fe atoms. The carbon nanotubes (CNTs) grown around Co-Fe alloy and Fe₃C nanoparticles exhibited a strong affinity to polysulfide species and superior catalytic capability as nano-reactors. The N-doping CNTs/carbon sheets (CS) facilitated the formation of Li₂S compound by promoting the Li⁺ ions transport while hindering the polysulfide shuttle effect. Hence, the issues of slow redox reactions and loss of polysulfide species were effectively rectified. As a result, the composite cathode FeCo/Fe₃C-CNC-based LSB delivered a good specific capacity of 1401 mAh g^-1 at 0.1C, and a low apacity fading rate of 0.029% per cycle at 1C. Besides, the structural stability of the FeCo/Fe₃C-CNC composite confirms its potential for the deployment in LSB applications.

Pt-NbC Composite as a Bifunctional Catalyst for Redox Transformation of Polysulfides in High-Rate-Performing Lithium-Sulfur Batteries

Accelerating the redox reaction of polysulfides via catalysis is an effective way to suppress the shuttling effect in lithium-sulfur (Li-S) cells. However, recent studies have mainly focused on the singular function of the catalyst, i.e., either oxidation or reduction of polysulfides. As such, the goal of rapid cycling of sulfur species remains to be highly desired. Herein, a Pt-carbide composite as a bifunctional catalyst was developed to simultaneously accelerate both the reduction of soluble polysulfides and the oxidation of insoluble Li₂S/Li₂S₂. Typically, a Pt-NbC composite was synthesized by growing Pt nanoparticles on the surface of NbC, and the resultant intimate interface in the hybrid is a key component for the bifunctional catalysis. During the reduction process, polysulfides could be grabbed on the surface of NbC via strong adsorption, and then these trapped polysulfides could be catalytically converted by Pt nanoparticles. During the oxidation process, both NbC and Pt exhibited catalytic activities for the dissolution of Li₂S. This process could lead to the renewal of the surface of the catalyst. By combining the sulfur cathode with a Pt-NbC-CNT (Pt-NbC anchored on a carbon nanotube)-coated separator, the cell was able to demonstrate a high initial capacity of 1382 mAh g^-1 at a current density of 0.2C. Furthermore, the cell was able to achieve an exceptional rate capability of 795 mAh g^-1 at 5C, and it was also able to show significantly inhibited self-discharge behavior. Thus, this work explores the catalyst design and the mechanism of a bifunctional catalyst for the performance enhancement in Li-S cells.

Boosted polysulfides regulation by iron carbide nanoparticles-embedded porous biomass-derived carbon toward superior lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are greatly expected to be the favored alternatives in the next-generation energy-storage technologies due to their exceptional advantages. However, the shuttle effect and sluggish reaction kinetics of polysulfides largely hamper the practical success of Li-S batteries. Herein, a unique iron carbide (Fe₃C) nanoparticles-embedded porous biomass-derived carbon (Fe₃C-PBC) is reported as the excellent immobilizer and promoter for polysulfides regulation. Such a distinctive composite strongly couples the vast active sites of Fe₃C nanoparticles and the conductive network of porous biomass-derived carbon. Therefore, Fe₃C-PBC is endowed with outstanding adsorptivity and catalytic effect toward inhibiting the shuttle effect and facilitating the redox kinetics of polysulfides, demonstrated by the detailed experimental demonstrations and theoretical calculation. With these synergistic effects, the Fe₃C-PBC/S electrode embraces a superb capacity retention of 82.7% at 2C over 500 cycles and an excellent areal capacity of 4.81 mAh cm^-2 under the high-sulfur loading of 5.2 mg cm^-2. This work will inspire the design of advanced hosts based on biomass materials for polysulfides regulation in pursuing the superior Li-S batteries.

Efficient Sulfur Host Based on Yolk-Shell Iron Oxide/Sulfide-Carbon Nanospindles for Lithium-Sulfur Batteries

Numerous nanostructured materials have been reported as efficient sulfur hosts to suppress the problematic "shuttling" of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries. However, direct comparison of these materials in their efficiency of suppressing LiPSs shuttling is challenging, owing to the structural and morphological differences between individual materials. This study introduces a simple route to synthesize a series of sulfur host materials with the same yolk-shell nanospindle morphology but tunable compositions (Fe3 O4 , FeS, or FeS2 ), which allows for a systematic investigation into the specific effect of chemical composition on the electrochemical performances of Li-S batteries. Among them, the S/FeS2 -C electrode exhibits the best performance and delivers an initial capacity of 877.6 mAh g-1 at 0.5 C with a retention ratio of 86.7 % after 350 cycles. This approach can also be extended to the optimization of materials for other functionalities and applications.

Superior lithium-storage properties derived from a g-C3N4-embedded honeycomb-shaped meso@mesoporous carbon nanofiber anode loaded with Fe2O3 for Li-ion batteries

In this work, a honeycomb-shaped meso@mesoporous carbon nanofiber material incorporating homogeneously dispersed ultra-fine Fe2O3 nanoparticles (denoted as Fe2O3@g-C3N4@H-MMCN) is synthesised through a pyrolysis process. The honeycomb-shaped configuration of the meso@mesoporous carbon nanofiber material derived from a natural bio-carbon source (crab shell) acts as a support for an anode material for Li-ion batteries. Graphitic carbon nitride (g-C3N4) is produced via the one-step pyrolysis of urea at high temperature under an N2 atmosphere without the assistance of additives. The resulting favorable electrochemical performance, with superior rate capabilities (1067 mA h g-1 at 1000 mA g-1), a remarkable specific capacity (1510 mA h g-1 at 100 mA g-1), and steady cycling performance (782.9 mA h g-1 after 500 cycles at 2000 mA g-1), benefitted from the advantages of both the host material and the Fe2O3 nanoparticles, which play an important role due to their ultra-fine particle size of 5 nm. The excellent cycle life and high capacity demonstrate that this strategy of strong synergistic effects represents a new pathway for pursuing high-electrochemical-performance materials for lithium-ion batteries.

Highly Graphitized Porous Carbon-FeNi3 Fabricated from Oleic Acid for Advanced Lithium-Sulfur Batteries

Improving the electrical conductivity of sulfur, suppressing shuttle/dissolution of polysulfide, and enhancing reaction kinetics in Li-S batteries are essential for practical applications. Here, for the first time, we have used inexpensive oleic acid as a single carbon source, and have added commercial SiO₂ as a template to form a porous structure, whereas introducing Fe(NO₃ )₃ and Ni(NO₃ )₂ as catalysts to increase the degree of graphitization. Moreover, the dual metal salts Fe(NO₃ )₃ and Ni(NO₃ )₂ can also form FeNi₃ alloy, and our results show that FeNi₃ nanoparticles accelerate the kinetic conversion reactions of polysulfide. By virtue of the well-developed porous structure and high degree of graphitization, the highly graphitized porous carbon-FeNi₃ (GPC-FeNi₃ ) has high conductivity to ensure fast charge transfer, and the hierarchically porous structure facilitates ion diffusion and traps polysulfide. Thus, a GPC-FeNi₃ /S cathode displays excellent electrochemical performance. At current rates of 0.2 and 1 C, a cathode of the GPC-FeNi₃ /S composite with a sulfur content of 70 % delivers high initial discharge capacities of 1108 and 880 mA h g^-1 , respectively, and retains reversible specific capacities of 850 mA h g^-1 after 200 cycles at 0.2 C and 625 mA h g^-1 after 400 cycles at 1 C.

Guidelines and trends for next-generation rechargeable lithium and lithium-ion batteries

This review article summarizes the current trends and provides guidelines towards next-generation rechargeable lithium and lithium-ion battery chemistries.