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Slow electrochemistry kinetics and dendrite growth are major obstacles for lithium-sulfur (Li-S) batteries. The investigations over the polymorph effect require more endeavors to further access the related catalyst design principles. Herein, the systematic evaluation of CoTe 2 alloy with two polymorphs regarding sulfur reduction reaction (SRR) and lithium plating/stripping is reported. As disclosed by theoretical calculations and electrochemical measurements, the orthorhombic (o-) and hexagonal (h-) CoTe 2 make a substantial difference. The reactivity origin of the CoTe 2 polymorphs is explored. The higher position of d-band centers for the Co atoms on the o-CoTe 2 leads to a higher displacement of the antibonding state; the lower antibonding state occupancy, the more effective the interaction with the sulfide moieties and lithium. Hence, o-CoTe 2 annihilates h-CoTe 2 and exhibits better catalysis and more uniform lithium deposition, consolidated by excellent performance of full cell made of o-CoTe 2 . It keeps stable charging/discharging for 800 cycles at 0.5 C with only 0.055% capacity decay per cycle and even achieves an areal capacity of 6.5 mAh cm -2 at lean electrolyte and high sulfur loading of 6.4 mg cm -2 . This work establishes the mechanistic perspective about the catalysts in Li-S batteries and provides new insight into the unified solution., (© 2023 Wiley-VCH GmbH.)

Currently, extensive research efforts are being devoted to suppressing the shuttle effect of polysulfides. The uncontrollable deposition of insulating Li 2 S onto the surface of sulfur host materials dramatically inhibits the continuous reduction of polysulfides in lithium-sulfur (Li-S) batteries. Herein, N,B co-doped hollow carbon microspheres embedded with dense FeSe-MnSe heterostructures and abundant Se vacancies (FeSe-MnSe/NBC) are rationally designed and synthesized via a facile hydrothermal reaction using ionic liquids as dopants. The introduction of abundant heterostructures subtly guides Li 2 S nucleation and deposition in 3D frameworks, thus avoiding the formation of the Li 2 S passivation layer and allowing for continuous Li + diffusion and subsequent nucleation of Li 2 S. Owing to these beneficial features, Li-S batteries comprising an FeSe-MnSe/NBC electrode exhibit significantly improved performance, including a high initial capacity of 1334 mAh g -1 at 0.2 C and ultralong cycle stability with a low capacity fading rate of 0.029% cycle -1 over 1000 cycles at 1.0 C. Remarkably, the FeSe-MnSe/NBC pouch cell delivers a considerable areal capacity of 3.6 mAh cm -2 at 0.1 C. This study provides valuable insight into heterostructures and Se vacancies for developing practical Li-S batteries., (© 2022 Wiley-VCH GmbH.)

Lithium-sulfur (Li-S) batteries are considered as one of the most promising next-generation rechargeable batteries owing to their high energy density and cost-effectiveness. However, the sluggish kinetics of the sulfur reduction reaction process, which is so far insufficiently explored, still impedes its practical application. Metal-organic frameworks (MOFs) are widely investigated as a sulfur immobilizer, but the interactions and catalytic activity of lithium polysulfides (LiPs) on metal nodes are weak due to the presence of organic ligands. Herein, a strategy to design quasi-MOF nanospheres, which contain a transition-state structure between the MOF and the metal oxide via controlled ligand exchange strategy, to serve as sulfur electrocatalyst, is presented. The quasi-MOF not only inherits the porous structure of the MOF, but also exposes abundant metal nodes to act as active sites, rendering strong LiPs absorbability. The reversible deligandation/ligandation of the quasi-MOF and its impact on the durability of the catalyst over the course of the electrochemical process is acknowledged, which confers a remarkable catalytic activity. Attributed to these structural advantages, the quasi-MOF delivers a decent discharge capacity and low capacity-fading rate over long-term cycling. This work not only offers insight into the rational design of quasi-MOF-based composites but also provides guidance for application in Li-S batteries., (© 2021 Wiley-VCH GmbH.)