Separator Membranes for Lithium–Sulfur Batteries: Design Principles, Structure, and Performance

Abstract

Improvement in electrical energy storage systems is one of the most recent research topics of great academic and industrial interest. Lithium‐sulfur (Li‐S) battery systems offer a theoretical energy density an order of magnitude larger than the popular Li‐ion batteries. The principle of working, inherent challenges in utilizing this system for commercial applications, and the various approaches taken to address these challenges are herein discussed in detail. The polysulfide shuttle effect is a major concern that deteriorates electrochemical performance in this system. In the recent past, electrodes have been intricately engineered to tackle this problem. However, more recently, the focus has shifted to the critical role of the separator. Modifying conventional separators or fabricating novel structures to enhance the cell performance appears to be a more feasible option. Some design principles that are critical to the functioning of a separator in Li‐S batteries, namely physisorption, chemisorption, and electrostatic repulsion, are discussed. Many recent papers proposed novel cell configurations with specifically designed functional separators. These reports are classified according to three design principles, analyzed critically, and compared with a view to assess their relative merits and efficacy. Some thoughts on the future directions in the development of an efficient separator are described.

Inhibition of Polysulfide Shuttles in Li–S Batteries: Modified Separators and Solid‐State Electrolytes

“…About functional separators, some design principles (physisorption, chemisorption, and electrostatic repulsion) were elaborated. [ 18 ] Besides, Yan et al [ 19 ] summarized interlayers and separators based on 2D materials. They inhibit polysulfide shuttle through physical confinement and chemical interactions.…”

On the Factors Affecting Aging and Self‐Discharge of Lithium–Sulfur Cells. Effect of Positive Electrode Composition

“…One of the most promising electrochemical systems is lithium–sulfur because it has a high theoretical specific energy of 2600 Wh kg −1 , which is in three to five times greater than the theoretical specific energy of electrochemical systems used in the current state‐of‐the‐art lithium‐ion batteries . In addition, sulfur is an abundant, low cost, and environmentally sustainable material .…”

“…In addition, sulfur is an abundant, low cost, and environmentally sustainable material . Studies on the development of lithium–sulfur batteries (LSBs) have been intensively conducted over the last decade …”

“…The main problems that prevent the release of LSBs to the market are the following: low compared with the expected value of specific energy (the specific energy of prototypes of LSBs is 300–400 Wh kg −1 instead of the expected 500–600 Wh kg −1 ), fast capacity depletion during cycling (usually, the average rate of capacity depletion is 0.05–0.1% per cycle instead of the required value, which is lower than 0.01–0.04% per cycle), high self‐discharge rate (5–15% per month instead of the desired 1–3% per month), and rapid aging during cycling and storage. The aging rate (the rate of irreversible capacity loss of LSBs during cycling and storage) can reach several percentage values per month.…”

“…Problems in the development of commercially acceptable LSBs are caused by the fact that LSBs are batteries with liquid cathodes because sulfur and lithium polysulfides, the active components of the positive electrode, are soluble in the electrolyte …”