Unraveling the Catalytic Activity of Fe–Based Compounds toward Li₂S_x in Li–S Chemical System from d–p Bands

Abstract

are not satisfactory because of the low conductivity of sulfur and extremely dissolving of lithium polysulfide (LPS) in ether-based electrolyte. [8] Adopting the structural carbon materials with abundant pores (e.g., carbon spheres, [9][10][11][12] carbon nanotubes, [13][14][15] graphene [16,17] ) and some metal-based compounds (such as cobalt, [6,18,19] nickel, [21][22][23][24] manganese, [25][26][27][28] iron [29][30][31][32][33][34][35][36][37] ) embedded in carbon host can remarkably improve the electrochemical performance of Li-S batteries. Recently, the researchers have demonstrated that configuring the interlayer between the separator and sulfur cathode is an effective way to alleviate the "shuttle effect" in Li-S redox system. [38][39][40][41][42] To avoid the heavy and large volume of the free-standing interlayer, people have begun to modify the separator with functional materials, such as structural carbon materials [43][44][45][46][47][48] and metal-based compounds. [49,50] As the typical earthabundant, low-cost, and environmentally friendly materials, iron-based compounds have already been widely researched in Li-S batteries. [51][52][53][54] For a long time, the researchers mainly ascribed the enhanced performance of Li-S batteries to strong absorbability of sulfur host materials to LPS (Li 2 S x , x = 1, 2, 4, 6, 8). However, according to the previous researches, [7,20] the binding energy of polar metal-based compounds toward LPS may not the decisive factor; relatively speaking, the catalyst effect of host materials toward LPS plays a leading role in improving the performance of Li-S batteries. Therefore, to better help researchers screen out modified materials suitable for sulfur cathode, it is particularly important to find a "descriptor" that can measure the catalytic ability of sulfur modified materials.Considering these factors, a series of iron-based particles (Fe 3 C@Fe 3 O 4 , Fe 3 O 4 , FeS, and Fe 3 N) embedded in the 3D graphitic carbon material were synthesized as the modified materials for battery separator via a facile two-step method. Among these Fe-based functional materials, the yolk-shell Fe 3 C@Fe 3 O 4 exhibits the best catalytical ability toward LPS in Li-S batteries. By analyzing electronic energy and structure, it has been discovered how the p and d band's center affects the electrochemical performance of Li-S batteries. Not only that, through the ab initio molecular dynamics (AIMD) simulations, it is also observed the dynamic changes of LPS clusters (Li 2 S 6 ) Lithium-sulfur batteries have ultra-high energy density and are considered to be one of the most promising energy storage systems among all battery systems. However, due to various thorny problems, their commercial production has not yet been realized. The current experimental research normally lacks a systematic investigation into the conversion mechanism of the sulfur cathode from the electronic structure level. Actually, there is still a lack of powerful theoretical guidance for the design of high-performance Li-S b...

Modulating Interband Energy Separation of Boron‐Doped Fe7S8/FeS2 Electrocatalysts to Boost Alkaline Hydrogen Evolution Reaction

“…To further support such a statement, the d-p models of related metal compounds were established. [13,14,18] In these metal compounds, the d-band electrons of a metal element and the p-band electrons of a non-metal element are known to play vital roles in forming and breaking the bonds with other intermediates or elements. [18] From the viewpoint of a valence band theory, the Fe-3d orbitals of a FeS based electrocatalyst overlap with the 3p orbitals of ligand S atoms, leading to the generation of a (FeS) bond and a (FeS)* anti-bond.…”

“…[13,14,18] In these metal compounds, the d-band electrons of a metal element and the p-band electrons of a non-metal element are known to play vital roles in forming and breaking the bonds with other intermediates or elements. [18] From the viewpoint of a valence band theory, the Fe-3d orbitals of a FeS based electrocatalyst overlap with the 3p orbitals of ligand S atoms, leading to the generation of a (FeS) bond and a (FeS)* anti-bond. [19] Stemming from different electronegativities of Fe and S atoms, the energy difference of a (FeS) bond from a (FeS)* anti-bond is thus induced, which can be described by the Δ dp of the band centers of Fe-3d (ε d ) and S-3p (ε p ).…”

Current Status and Challenges of Calcium Metal Batteries

“…Various graphitic carbon, if the defects, pore and surface, and phase structure are rationally engineered, is another type of promising cathode material, based on an anion–cation relay storage mechanism. [ 2,22–27 ] Hence, the future trends in cathode materials lie in not only achieving cycling stability and long lifespan of S and sulfides, [ 28,29 ] layered metal oxides, [ 30 ] and polyanionic phosphates but also developing multicomponent high‐voltage or Ca‐rich large capacity cathodes such as Ni/Mn‐based Li/Na‐counterparts and defect/interface‐engineered fast kinetics and cycling‐stable cathodes. [ 31–36 ]…”

“…Various graphitic carbon, if the defects, pore and surface, and phase structure are rationally engineered, is another type of promising cathode material, based on an anion-cation relay storage mechanism. [2,[22][23][24][25][26][27] Hence, the future trends in cathode materials lie in not only achieving cycling stability and long lifespan of S and sulfides, [28,29] layered metal oxides, [30] and Current calcium metal batteries and future trends from voltage-capacity-efficiency's view, in which the redox potentials for cathodes and Cametals, as well as some reference electrodes frequently involved in the research of calcium batteries, are calibrated to versus SHE. All the data are adapted from publications reported previously.…”

Polysulfide Catalytic Materials for Fast‐Kinetic Metal–Sulfur Batteries: Principles and Active Centers

“…Moreover, Fe 3 C@Fe 3 O 4 @C was utilized as the interfacial coating catalyst on the separator to promote the conversion of lithium polysulfides. [ 144 ] Based on the prepared materials, the d–p band models have been successfully employed to simulate the Fe‐based polysulfide catalysts for LiS batteries. The narrower energy bandgap (∆p–d), that is, the average difference within the center of the p‐band and the d‐band in the electron spin upward/downward, corresponds to a reduced reaction impediment and improved rate‐performance of batteries.…”