Addressing the Prominent Li⁺ Intercalation Process of Metal Sulfide Catalyst in Li‐S Batteries

Abstract

and its discharge products (Li 2 S 2 /Li 2 S) are poor and will largely hinder the reaction kinetics of Li-S system; while the dissolution and migration of lithium polysulfides (LiPS) will lead to undesired shuttle effects and poor cycle life, all of which will hamper the large scale application of Li-S batteries. [7][8][9] In the view of the above problems, scientists have done a lot of exploration on improving the reaction dynamics. A series of carbon materials, such as meso/ microporous carbon, carbon nanotubes and graphene, are widely used to remission the shuttle effect of Li-S batteries, which can provide conductive framework, alleviate the volume change of electrodes, and physically constrain LiPS. [10] However, the physical encapsulation of the nonpolar carbon-based sulfur host is not effective enough to restrain the shuttle effect. A common practice in the research of Li-S batteries is the adoption of different catalysts to boost its conversion chemistry. An effective way to solve this problem is to use polar metal compounds, such as transition metal oxides, [11][12][13] nitride [14] and sulfides, [15][16][17] to improve the hydrophobic interface of carbon materials and provide extra chemical adsorption effect. Transition metal sulfides, such as CoS 2 , MoS 2 and VS 4 , are most welcomed catalysts, which not only possess good conductivity and intensive affinity for LiPS, but also show great potential in LiPS adsorption and catalysis effect for the key reactions of Li-S battery. [18] Various catalysts are adopted to boost the conversion chemistry of Lithium sulfur (Li-S) batteries, but most of them are electrochemical-active in a working Li-S cell, and the changes of their chemical state and the induced influence toward the Li-S catalytic mechanism are unclear. Herein, a dynamic catalytic mechanism is proposed by the selection of Li + -interaction-reversible VS 2 catalyst as a representative species to address this issue. The VS 2 catalyst with ultrastable Li + intercalation/deintercalation characteristics, fast charge transport capability, and active capacity contribution can provide a strong and dynamic chemisorption toward polysulfide (LiPS). The resulting Li-S batteries exhibit excellent cyclability at 3 C with capacity attenuation of 81.23% over 250 cycles and good rate capability up to 8 C. Moreover, a new insight toward the dynamic catalytic changes induced by the prominent Li + intercalation process of metal sulfide is proposed, which can provide more opportunities for the evolutional design for Li-S catalysts.

Insight into the Catalytic Role of Defect-Enriched Vanadium Sulfide for Regulating the Adsorption–Catalytic Conversion Behavior of Polysulfides in Li–S Batteries

“…In Li–S batteries, most reported electrocatalysts are nonchemically active and do not participate in electrochemical reactions. However, the VS 2 catalyst is different from them, in that it has typical electrochemical behaviors of lithiation and delithiation, and the Li x VS 2 intermediates play an important role in regulating polysulfide conversion . According to the previous reported work, the S vacancies in VS 2 can provide an additional transfer path that is perpendicular to the VS 2 plane and improve the ion-diffusion kinetics in VS 2– x , so it is inferred that VS 2– x can likely have high catalytic activity, which is also verified by electrochemical tests.…”

“…However, unlike other materials, layered VS 2 catalysts have typical lithiation behavior, and the relevant lithiation potentials are in the working voltage range of Li–S, which should not be ignored. Unfortunately, most papers reporting VS 2 catalysts as nonchemically active components did not consider their dynamic evolution behavior − until Wang et al reported the prominent Li + intercalation process of VS 2 in Li–S batteries . According to a previous report, Li et al reported that the Li x Mo 6 S 8 intermediate shows a higher affinity to polysulfides than the original Mo 6 S 8 and thus displays strong adsorbability and good catalysis to polysulfides .…”

Modulating Bond Interactions and Interface Microenvironments between Polysulfide and Catalysts toward Advanced Metal–Sulfur Batteries

“…[ 56 ] Very recently, the VS 2 has also been explored to show the same mechanism when used as a polysulfide regulator. [ 57 ] In addition to metal sulfides, some pseudocapacitive metal oxides also show similar properties. For example, orthorhombic Nb 2 O 5 and birnessite MnO 2 were applied as desirable electron/ion sources during the chemical redox reactions of sulfur.…”

Cobalt Vanadate (Co3V2O8) Hollow Microspheres as a Polysulfide Adsorption and Conversion Catalyst for Li–S Batteries

“…To mitigate the shuttle effect and improve the reaction kinetics, researchers investigated several metal-based (metal, metal oxides/sulfides/nitrates, etc.) and metal-free adsorbents as catalytic additives. − In this regard, metal oxides with mixed oxidation states were found to be suitable cost-effective polysulfide adsorption and conversion catalysts as the metal centers and polar O 2‑ sites chemically interact with LiPS. − Particularly, the metal oxides with hollow structures could efficiently trap polysulfides through strong physical and chemisorption. Further, the inner void space of the hollow sphere accommodates large volume changes during the charge–discharge process. , Gao et al reported V 2 O 5 (V-metal center) hollow microspheres with graphene carbon network heterostructures as cathode hosts for Li–S batteries.…”