Li/S

Abstract

Lithium–sulfur batteries are among the most promising energy‐storage devices because of their high charge‐storage capacity, low cost, and the wide availability of sulfur. Thus, it is essential to develop the potential of lithium–sulfur cells as a next‐generation rechargeable energy‐storage technology and transition them into practical battery systems. However, the design of high‐energy‐density lithium–sulfur batteries with long‐term stability has encountered significant challenges due to the intrinsic materials characteristics (e.g. insulating nature of sulfur, irreversible polysulfide relocation, volume change of sulfur, lithium anode degradation, low electrolyte stability, and electrode degradation). Over the past 20 years, efforts to improve the battery performance and chemistry have resulted in new scientific insights, indicating that the electrochemical performance of lithium–sulfur system and its intrinsic materials challenges are further aggravated by several extrinsic technical conditions, including the cell‐fabrication parameters (e.g. the amount of sulfur, electrolyte, and lithium metal used) and the cell‐testing conditions (e.g. operating voltage window, testing temperature, and cycle rates). In order to successfully bring the lithium–sulfur battery technology to the market, we need to focus on developing high‐loading sulfur cathodes under lean electrolyte and controlled excess lithium conditions. However, it has proven extremely challenging to develop a cell that simultaneously satisfies these metrics while also displaying acceptable high electrochemical efficiency and stability. To understand these issues, the fundamental conversion battery chemistry and issues associated with lithium–sulfur system, particularly in terms of the intrinsic materials characteristics and extrinsic technical conditions are discussed in this article.

Current Status and Future Prospects of Metal–Sulfur Batteries

“…One possibility for enhancing the positive properties of polysulfides is to develop a suitable cathode configuration for hosting polysulfides within the cathode region. Currently, the research community has proposed several promising cell configurations, such as interlayers, coated separators, and porous current collectors . Another possible route is the development of better electrolytes, such as optimizing the electrolyte solvent and/or salt, application of organic electrolyte containing high salt concentration (e.g., >1.0 m ), and liquid ionic electrolytes with additives .…”

“…Ideally, maintaining an appropriate void in the electrode could improve the tolerance to volume changes of the active material and maintain the cathode integration . However, sulfur has an innate low volumetric energy density, and a high void cathode configuration would further diminish the volumetric energy density .…”

“…These engineered nanocomposites72,203b and modified cell components (e.g., separator and cathode structure) deliver a peak charge‐storage capacity of over 1600 mA h mg −1 . Long cyclabilities of over 1000 cycles have been demonstrated with numerous, various composite cathodes, interlayers, porous cathode substrates, sandwiched cathode configurations, and coated separators . Better electrochemical characteristics have also been realized by integrating newly developed cell components, such as the application of sulfur/carbon nanocomposites in the cathode with either a TiO 2 /TiN coating205h or a MoSe 2 /reduced graphene oxide coating on the separator ( Figure a,b) 206b…”

Progress on the Critical Parameters for Lithium–Sulfur Batteries to be Practically Viable

“…Starting in 2012, researchers began to design new cell components with various 3D cathode architectures that more effectively utilize the unique solid–liquid–solid phase transitions between sulfur, polysulfide, and sulfide during the redox reactions of the lithium–sulfur cells. Such 3D battery components, including porous current collectors in the cathode, interlayers between the cathode and the separator, coated separators with a carbon or polymer coating facing the cathode, sandwiched cathodes possessing a layer of active material between two carbon layers, multilayered cathodes integrating layered sandwiched cathodes, and core–shell cathodes, are based on an active‐material reservoir to form the cathode substrate as well as a polysulfide‐trapping barrier to confine polysulfides within the cathode region …”

“…Hosting and trapping the active material within the 3D cathode architecture initiated the early‐stage design of high‐loading sulfur cathodes. They are currently the mainstream in fabricating high‐loading sulfur cathodes for achieving enhanced electrochemical performances and for understanding the remaining challenges in lithium–sulfur technology . These newly designed lithium–sulfur cell components are mainly made with robust conductive substrates (e.g., carbon‐based substrates and composites with functional polymers and oxides) having strong mechanical strength, tenacity, and flexibility .…”