Design Rules of a Sulfur Redox Electrocatalyst for Lithium–Sulfur Batteries

Abstract

However, the shuttle effect triggered by the dissolution of long-chain polysulfides (Li 2 S x , 4 ≤ x ≤ 8) results in severe active sulfur loss and fast capacity decay, which severely hinders the commercial application of these batteries. [4,6] Fundamentally, these problems are a result of the slow and complex sulfur reduction reaction (SRR), i.e., the sluggish kinetic transformation of soluble lithium polysulfides (LiPSs) to insoluble Li 2 S 2 /Li 2 S (discharge products). [7,8] Therefore, exploring effective strategies to accelerate the conversion of LiPSs from the liquid to the solid state is essential to boost the practical energy density and lifespan of lithium-sulfur batteries. [9,10] Considerable efforts have been devoted to addressing the aforementioned problems, typically by using sulfides, nitrides, phosphides as host materials to trap the LiPSs in the sulfur cathode. [11][12][13][14] However, these physical or electrostatic confinement/trapping methods fail to entirely avoid the dissolution and accumulation of LiPSs in the electrolyte. [8] A catalytic approach has therefore been proposed as a more proactive solution to cure the shuttle effect by accelerating the conversion of the liquid-phase long-chain LiPSs into final solid-phase discharge products. [15,16] Like the oxygen Seeking an electrochemical catalyst to accelerate the liquid-to-solid conversion of soluble lithium polysulfides to insoluble products is crucial to inhibit the shuttle effect in lithium-sulfur (Li-S) batteries and thus increase their practical energy density. Mn-based mullite (SmMn 2 O 5 ) is used as a model catalyst for the sulfur redox reaction to show how the design rules involving lattice matching and 3d-orbital selection improve catalyst performance. Theoretical simulation shows that the positions of Mn and O active sites on the (001) surface are a good match with those of Li and S atoms in polysulfides, resulting in their tight anchoring to each other. Fundamentally, dz 2 and dx 2 −y 2 around the Fermi level are found to be crucial for strongly coupling with the p-orbitals of the polysulfides and thus decreasing the redox overpotential. Following the theoretical calculation, SmMn 2 O 5 catalyst is synthesized and used as an interlayer in a Li-S battery. The resulted battery has a high cycling stability over 1500 cycles at 0.5 C and more promisingly a high areal capacity of 7.5 mAh cm −2 is achieved with a sulfur loading of ≈5.6 mg cm −2 under the condition of a low electrolyte/sulfur (E/S) value ≈4.6 µL mg −1 .

Li2S4 Anchoring Governs the Catalytic Sulfur Reduction on Defective SmMn2O5 in Lithium–Sulfur Battery

“…In our previous work, we have found that the distance between active sites Mn and O atoms (3.138 Å) on the exposed low-index surface matches well with that of S and Li atoms (3.252 Å) in polysulfides (LiPSs) with a high lattice matching ratio of 96.5%, leading to a strong anchoring to LiPSs. And further systematic experimental measurements have shown that a Li-S battery with a SmMn 2 O 5 interlayer has a remarkable catalytic activity and high cycling stability with a capacity decay rate as low as 0.04% per cycle over 1500 cycles at 0.5 C. [23] However, the physical origin of the modulation of LiPS anchoring by lattice matching is inaccessible. Different from oxygen reduction reaction (ORR), the key questions about the interplay among LiPSs and the theoretical limitation of SRR overpotential remain open to discussion.…”

Theoretical and Experimental Understanding of Metal Single-Atom Electrocatalysts for Accelerating the Electrochemical Reaction of Lithium–Sulfur Batteries

“…The low electronic/ionic conductivity of sulfur and the discharged products leads to sluggish conversion of polysulfide intermediates and inadequate utilization of sulfur . In addition, the shuttle effect caused by the dissolution and migration of high-order polysulfides will result in fast decay of irreversible capacity and Coulombic efficiency. , Therefore, to improve the performance of Li–S batteries, it is highly desirable to develop an effective strategy to immobilize the polysulfides and propel the kinetic conversion between polysulfides and Li 2 S 2 /Li 2 S. − …”

CoSe Nanoparticle Embedded B,N-Codoped Carbon Nanotube Array as a Dual-Functional Host for a High-Performance Li-S Full Battery

“…The employment of advanced Li hosts has been demonstrated to be the most simple and effective way to induce planar Li deposition. Porous carbonaceous materials have been recognized as promising Li hosts, which have been attributed to a large amount of pore structures, good electrical conductivity, and high structural stability . However, Li metal cannot be deposited evenly on the carbon frameworks due to the lithiophobic property of carbonaceous hosts. − Recently, a series of polar lithiophilic materials such as W 2 C, TiN-VN, and V 8 C 7 -VO 2 have been integrated in carbon-based materials to induce uniform Li deposition.…”