TitleA long-life, high-rate lithium/sulfur cell: A multifaceted approach to enhancing cell performance Permalink https://escholarship.org/uc/item/97z815sv Journal Nano Letters, 13(12)

In this review, we begin with a brief discussion of the operating principles and scientific/technical challenges faced by the development of lithium/sulfur cells. We then introduce some recent progress in exploring cathodes, anodes, and electrolytes for lithium/sulfur cells. In particular, several effective strategies used to enhance energy/power density, obtain good efficiencies, and prolong cycle life will be highlighted. We also discuss recent advancements in techniques for investigating electrode reactions in real time and monitoring structural/morphological changes of electrode materials under cell operating conditions to gain a better understanding of the mechanistic details of electrode processes. Finally, the opportunities and perspective for future research directions will be discussed.

With a theoretical capacity of 1166 mA·h·g(-1), lithium sulfide (Li(2)S) has received much attention as a promising cathode material for high specific energy lithium/sulfur cells. However, the insulating nature of Li(2)S prevents the achievement of high utilization (or high capacity) and good rate capability. Various efforts have been made to ameliorate this problem by improving the contact between Li(2)S and electronic conductors. In the literature, however, a relatively high capacity was only obtained with the Li(2)S content below 50 wt %; therefore, the estimated cell specific energy values are often below 350 W·h·kg(-1), which is insufficient to meet the ever-increasing requirements of newly emerging technologies. Here, we report a cost-effective way of preparing nanostructured Li(2)S-carbon composite cathodes by high-energy dry ball milling of commercially available micrometer-sized Li(2)S powder together with carbon additives. A simple but effective electrochemical activation process was used to dramatically improve the utilization and reversibility of the Li(2)S-C electrodes, which was confirmed by cyclic voltammetry and electrochemical impedance spectroscopy. We further improved the cycling stability of the Li(2)S-C electrodes by adding multiwalled carbon nanotubes to the nanocomposites. With a very high specific capacity of 1144 mA·h·g(-1) (98% of the theoretical value) obtained at a high Li(2)S content (67.5 wt %), the estimated specific energy of our cell was ∼610 W·h·kg(-1), which is the highest demonstrated so far for the Li/Li(2)S cells. The cells also maintained good rate capability and improved cycle life. With further improvement in capacity retention, nanostructured Li(2)S-C composite cathodes may offer a significant opportunity for the development of rechargeable cells with a much higher specific energy.