Research Progress toward the Practical Applications of Lithium-Sulfur Batteries.

The renaissance of Li-S battery technology is evidenced by the intensive R&D efforts in recent years. Although the theoretical capacity and energy of a Li-S battery is theoretically very high, the projected usable energy is expected to be no more than twice that of state-of-the-art Li-ion batteries, or 500 Wh/kg. The recent "sulfur fever" has certainly gathered new knowledge on sulfur chemistry and electrochemistry, electrolytes, lithium metal, and their interactions in this "new" system; however, a real advance toward a practical Li-S battery is still missing. One of the main reasons behind this is the sensitivity of Li-S batteries to the experimental testing parameters. Sophisticated nanostructures are usually employed, while the practicality of these nanomaterials for batteries is rarely discussed. The sulfur electrode, usually engineered in a thin-film configuration, further poses uncertainties in the knowledge transfer from the lab to industry. This review article briefly overviews the recent research progress on Li-S batteries, followed by a discussion of the Li-S battery system from the authors' own understandings collected from their past few years of research. The critical findings, the unresolved issues, and the scientific gap between lab research and industrial application are discussed. The future work in Li-S battery research is also explored to propel relevant research efforts toward industrial applications.