Anionic Redox Chemistry in Polysulfide Electrode Materials for Rechargeable Batteries

Abstract

Classical Li-ion battery technology is based on the insertion of lithium ions into cathode materials involving metal (cationic) redox reactions. However, this vision is now being reconsidered, as many new-generation electrode materials with enhanced reversible capacities operate through combined cationic and anionic (non-metal) reversible redox processes or even exclusively through anionic redox transformations. Anionic participation in the redox reactions is observed in materials with more pronounced covalency, which is less typical for oxides, but quite common for phosphides or chalcogenides. In this Concept, we would like to draw the reader's attention to this new idea, especially, as it applies to transition-metal polychalcogenides, such as FeS , VS , TiS , NbS , TiS , MoS , etc., in which the key role is played by the (S-S) /2 S redox reaction. The exploration and better understanding of the anion-driven chemistry is important for designing advanced materials for battery and other energy-related applications.

Expediting redox kinetics of sulfur species by atomic‐scale electrocatalysts in lithium–sulfur batteries

“…Powering the rapid LiPS conversion is critically important to realize high‐capacity, fast‐charge, and long‐term Li–S batteries. Based on these considerations, various electrocatalysts are applied in a working Li–S battery . However, most of them suffer from low surface‐to‐volume ratio, considerably sacrificing the electrocatalytic activities.…”

“…Based on these considerations, various electrocatalysts are applied in a working Li-S battery. [78][79][80][81][82][83][84] However, most of them suffer from low surface-to-volume ratio, considerably sacrificing the electrocatalytic activities. Atomic-scale electrocatalysts are preferred in this respect, as they take advantages of atomic efficiency of electrocatalysts to modulate the LiPS electrochemical behaviors.…”

Revealing the Flexible 1D Primary and Globular Secondary Structures of Sulfur‐Rich Amorphous Transition Metal Polysulfides

“…[8c] When used as battery electrodes, transition metal polysulfides are noted for the absence of the infamous Li 2 S x polysulfide "shuttle effect" and for unusual operation mechanisms related to additional redox processes in the anionic disulfide groups (SÀ S) 2À + 2e⇄2 S 2À , which we covered in our recent paper. [12] Similar activity of disulfide groups is expected in catalytic processes. [13] Among the amorphous transition metal polysulfides, MoS 3 is probably the most studied material.…”

“…For example, MoS 3.4 chalcogels deliver high gravimetric capacities of over 600 mAh g −1 in lithium‐ion battery (LIB) cathodes, while for MoS 5.7 this value is even higher (746 mAh g −1 ) . When used as battery electrodes, transition metal polysulfides are noted for the absence of the infamous Li 2 S x polysulfide “shuttle effect” and for unusual operation mechanisms related to additional redox processes in the anionic disulfide groups (S−S) 2− +2e⇄2 S 2− , which we covered in our recent paper . Similar activity of disulfide groups is expected in catalytic processes …”

A Perspective on Energy Densities of Rechargeable Li‐S Batteries and Alternative Sulfur‐Based Cathode Materials

“…Recently, metal polysulfides (e.g., MS x , M = Ti, Mo, or Co, and x > 3) have appeared to be an interesting class of high‐capacity materials . It can be classified as another series of alternative sulfur cathode materials.…”