Regulating Electronic Structure of Fe–N₄ Single Atomic Catalyst via Neighboring Sulfur Doping for High Performance Lithium–Sulfur Batteries

Abstract

Constructing high performance electrocatalysts for lithium polysulfides (LiPSs) adsorption and fast conversion is the effective way to boost practical energy density and cycle life of rechargeable lithium–sulfur (Li–S) batteries, which have been regarded as the most promising next generation high energy density battery but still suffering from LiPSs shuttle effect and slow sulfur redox kinetics. Herein, a single atomic catalyst of Fe–N4 moiety doping periphery with S (Fe–NSC) is theoretically and experimentally demonstrated to enhance LiPSs adsorption and facilitated sulfur conversion, due to more charge density accumulated around Fe–NSC configuration relative to bare Fe–N4 moiety. Thereafter, the graphene oxide supported Fe–NSC catalyst (Fe–NSC@GO) is modified to the commercial separator through a simple slurry casting method. Thus, Li–S cells with Fe–NSC@GO modified separators display high discharge capacity and excellent cyclability, showing 1156 mAh g−1 at 1 C rate and a low capacity decay of only 0.022% per cycle over 1000 cycles. Even with a high sulfur loading of 5.1 mg cm−2, the cell still delivers excellent cycling stability. This work provides a fresh insight into electrocatalyst structural tuning to improve the electrochemical performance of Li–S batteries.

Atomically Dispersed Fe–N4 and Ni–N4 Independent Sites Enable Bidirectional Sulfur Redox Electrocatalysis

“…Theoretical simulation on Ti, V, Cr, and Mn with four nitrogen atom coordination (M–N 4 ) showed strong SAC–S bonds and simultaneously weakened S–S bonds in LiPSs . Apart from the LiPSs shuttling suppression, the reaction rate for the charging process is highly determined by the oxidation of insulating Li 2 S. An insufficient catalytic effect will cause surface passivation and lower the sulfur utilization. , Progress has been achieved in enhancing the catalytic activity (especially for sulfur reduction) by regulating the coordinated ligands or controlling the distance of the SAC sites. − Nevertheless, achieving a fast bidirectional sulfur conversion process by using a single metal atom catalyst is challenging. Recently, constructing dual-atom catalysts (DACs) also has been reported as an effective strategy to propel the kinetics of oxygen reduction reaction and polysulfides conversion by tailoring the electronic structure of metal centers. , Compared with coordination engineering of the SACs and electron structure modulation of the DACs, the appropriate selection of independent dual single atoms to separate sulfur oxidation and reduction could offer a viable approach toward a high catalytic effect, which has not been reported.…”

Building Up an “Elemental Property—Adsorption Energy Descriptor—Decomposition Barrier” Three‐Tier Model for Screening Biatom Catalysts in Sodium–Sulfur Batteries

“…For Na 2 S adsorbed on the M-Cr@N-C systems (Figure S11 The coordination atoms of the central metal atoms also play important roles in their catalytic activity and cannot be neglected. [15,19] Here, we discuss the effect of replacing one of the surrounding coordination atoms (N) by C, S, or O atoms for the above-mentioned 10 systems with E b <1 eV (V 2 @N-C, Cr 2 @N-C, W-V@N-C, Mo-V@N-C, Cr-V@N-C, Os-V@N-C, Co-V@N-C, W-Cr@N-C, Mo-Cr@N-C, and Ti-Cr@N-C) (Figure S14, Supporting Information). The descriptor E diff we used to predict Na 2 S decomposition barriers are still highly applicable to these 90 G-BACs with new coordination environments and some of them even exhibit better catalytic performance, such as Mo-V@S (2) -N-C, and V 2 @O (1) -N-C (Figure S15, Supporting Information).…”

Vanadium as Auxiliary for Fe–V Dual-Atom Electrocatalyst in Lithium–Sulfur Batteries: “3D in 2D” Morphology Inducer and Coordination Structure Regulator

“…However, the implementation of Fe SAMCs in LSBs still faces several main problems: (i) The ordinarily plane-symmetric Fe–N 4 centers with relatively weak polarity are unfavorable for anchoring LiPSs. , Cui’s group experimentally and theoretically investigated the LiPSs’ anchoring effect of different single-atom metal–N 4 sites (metal = Fe, Mn, Ru, Zn, Co, and V) loaded on nitrogen-doped graphene (NG) and found that the binding energy for Li 2 S 6 on several single-atom metals (metal = Fe, Mn, Ru, Zn, and Co) slightly differs from that on NG, while the single V atom catalyst shows the prominently highest binding energy toward Li 2 S 6 and the smallest Li 2 S decomposition barrier . (ii) The catalytic role of Fe–N 4 centers may be limited by the intrinsic configuration, which could be settled by engineering heterometal atoms, , altering the coordination elements, − or regulating N coordination numbers. , (iii) The carbon substrate of single Fe atoms mostly present single dimensional morphology (3D/2D), which cannot combine the advantages of different dimensions for charge transfer and confined sulfur reaction. , (iv) Most methods for synthesizing Fe SAMCs on a carbon matrix require high-temperature pyrolysis, in which excess Fe atoms in the precursor tend to aggregate and form uncontrollable graphite-wrapped Fe 3 C particles via catalytic graphitization, leading to undesirable metal agglomeration and structure turbulence. , Therefore, it is necessary to develop auxiliaries that could regulate the local coordination environment of metal atoms, optimize the substrate morphology, and reduce the agglomeration of metal atoms simultaneously, thus optimizing the adsorption and catalysis role of atomic electrocatalysts toward LiPSs. There has rarely been research focused on this point up to now.…”