The Progress of Li–S Batteries—Understanding of the Sulfur Redox Mechanism: Dissolved Polysulfide Ions in the Electrolytes

Abstract

Rechargeable lithium-sulfur batteries have aroused great attention in the recent years. Thousands of research articles have been published, and among those publications the majority are dedicated to improving the battery's performance through chemically and physically modifying the sulfur electrode, electrolytes, separator, and lithium anode. However, the single most important aspect, understanding the sulfur redox mechanism is sparse and overwhelmed by the huge volume of work This article is protected by copyright. All rights reserved. 2 done on improving the battery's performance. Besides the intrinsic complexity of the sulfur redox chemistry, the most challenging task is to find an effective analytical technique for the quantitative and qualitative determination of the dissolved and solid polysulfides, including elemental sulfur. In this paper, the recent important research aiming to understand the redox mechanism of the sulfur electrode is reviewed in light of the unique analytical techniques used in the research. The review re-affirms the complexity of the sulfur redox chemistry and lays the background for the future mechanistic research for Li-S batteries.

A Highly Conductive MOF of Graphene Analogue Ni3(HITP)2 as a Sulfur Host for High‐Performance Lithium–Sulfur Batteries

“…In fact, the cycling stability and rate performance of Li–S batteries are related to the Li + diffusion and interfacial charge transfer process. It is noted that the charge reaction mechanism is not the reverse of the discharge mechanism in Li–S systems . Therefore, the investigation of reaction kinetics at a different stage was necessary and CV measurements were carried out at various scanning rates from 0.1 to 0.7 mV s −1 .…”

Lithium–Sulfur Batteries under Lean Electrolyte Conditions: Challenges and Opportunities

“…[29] The dissolved polysulfides serve as an intrinsic redox mediator to activate deactivated solid sulfur and Li 2 S through a chemical pathway (commonly disproportionation and comproportionation reactions), thereby increasing the utilization of sulfur. [30] However, high polysulfide solubility in electrolyte induces other concerns including the redox-shuttling between the cathode and the anode, the loss of active materials, as well as the parasitic reactions at the Li anode. [31] Under low E/S ratio conditions, the advantages of solvated polysulfides are suppressed and the disadvantages are amplified, making the challenging operation of lean-electrolyte Li-S battery.…”

Ultrafine Co3Se4 Nanoparticles in Nitrogen‐Doped 3D Carbon Matrix for High‐Stable and Long‐Cycle‐Life Lithium Sulfur Batteries

“…[ 4 ] However, up to now, LSBs are yet to meet commercial demand mainly due to their unstable long‐cycling performance and related safety concerns that stem from the electronic/ionic inertia of sulfur/lithium sulfides (Li 2 S) in the cathode and complex lithium polysulfide (LiPS) shuttle reactions in the ether‐based electrolyte as well as the unevenly plating/depositing of lithium in the anode. [ 5–8 ]…”

“…However, this steady behavior could be only a passing fancy on account of the long time discharge stage in practical applications where the impact of polysulfide shuttle tends to be magnified at least several times. [ 7,9,10 ] Evidenced by the fact that current pouch cells with energy density exceeding 300 Wh kg −1 in LSB systems afford shorter stable lifespan for less than 100 cycles. [ 12 ]…”