Catalytic Effect of Ammonium Thiosulfate as a Bifunctional Electrolyte Additive for Regulating Redox Kinetics in Lithium–Sulfur Batteries by Altering the Reaction Pathway

Abstract

Sluggish sulfur redox kinetics and incessant shuttling of lithium polysulfides (LiPSs) greatly influence the electrochemical properties of lithium−sulfur (Li−S) batteries and their practical applications. For this reason, ammonium thiosulfate (AMTS) with effective redox regulation capability has been proposed as a functional electrolyte additive to promote the bidirectional conversion of sulfur species and inhibit the shuttle effect of soluble LiPSs. During discharging, the S 2 O 3 2− in AMTS can trigger the rapid reduction of LiPSs from long chains to short chains by a spontaneous chemical reaction with sulfur species, thereby decreasing the accumulation of LiPSs in the electrolyte. During charging, the NH 4 + in the AMTS enhances the dissociation/dissolution of Li 2 S 2 /Li 2 S by hydrogen-binding interactions, which alleviates the electrode surface passivation and facilitates the reversible oxidation of short-chain sulfides back to long chains. The enhanced bidirectional redox kinetics brought about by AMTS endows Li−S cells with high reversible capacity, excellent cycle stability, and rate capability even under lean electrolyte conditions. This work not only illustrates an effective redox regulation strategy by an electrolyte additive but also investigates its catalytic reaction mechanism and Li corrosion behavior. The crucial criteria for screening additives that enable bidirectional redox mediation analogous to AMTS are summarized, and its application perspectives/challenges are further discussed.

Nano‐LaMnO3 Modified Separator for Enhanced Redox Reaction Kinetics and Electrochemical Performance of Lithium‐Sulfur Batteries

“…Lithium-sulfur (LiÀ S) battery with high theoretical energy density (~2600 Wh kg À 1 ) and abundant material resource is considered to be a promising candidate for next-generation rechargeable batteries. [1,2] Unfortunately, there are still many challenges hindering its practical application, e. g., insulating nature of sulfur and discharge product Li 2 S 2 /Li 2 S restricting their electrochemical activity, and "shuttle effect" of soluble intermediates polysulfides (Li 2 S x , 4 � x � 8) resulting in the loss of active materials, rapid capacity degradation and severe Li corrosion. [3][4][5] Various strategies have been attempted for settling above problems such as electrolyte component optimization, cathode composite construction and functional design of cell structure.…”