Single-atom site catalysis in Li-S batteries.

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

An Endogenous Prompting Mechanism for Sulfur Conversions Via Coupling with Polysulfides in Li-S Batteries.

The sluggish kinetics process and shuttling of soluble intermediates present in complex conversion between sulfur and lithium sulfide severely limit the practical application of lithium-sulfur batteries. Herein, by introducing a designated functional organic molecule to couple with polysulfide intermediators, an endogenous prompting mechanism of sulfur conversions has thus been created leading to an alternative sulfur-electrode process, in another words, to build a fast "internal cycle" of promotors that can promote the slow "external cycle" of sulfur conversions. The coupling-intermediators between the functional organic molecule and polysulfides, organophosphorus polysulfides, to be the "promotors" for sulfur conversions, are not only insoluble in the electrolyte but also with higher redox-activity. So the sulfur-electrode process kinetics is greatly improved and the shuttle effect is eliminated simultaneously by this strategy. Meanwhile, with the endogenous prompting mechanism, the morphology of the final discharge product can be modified into a uniform covering film, which is more conducive to its decomposition when charging. Benefiting from the effective mediation of reaction kinetics and control of intermediates solubility, the lithium-sulfur batteries can act out excellent rate performance and cycling stability.

Diversity-oriented synthesis of imidazo[2,1-a]isoquinolines.

Herein, we report an efficient and practical strategy for the synthesis of five types of imidazo[2,1-a]isoquinolines via Cp*RhIII-catalyzed [4+2] annulation of 2-arylimidazoles and α-diazoketoesters, whose structural and substituted diversity at 5- or 6-position can be precisely controlled by the α-diazoketoester coupling partners. Compared with previous reports, in this study, we merged two attractive C-C cleavage strategies (retro-Claisen and decarboxylation) into the classical C-H functionalization/condensation process by choosing appropriate ester groups (-COOEt, -COOtBu or -COOiPr) or inexpensive additives (HOAc or KOAc). Moreover, the synthetic efficacies of these methods were demonstrated by the concise synthesis of several bioactive compounds and the late-stage modification of representative drugs.