Atomistic Scale Modeling of Anode/Electrolyte Interfaces in Li-Ion Batteries.

A key issue in lithium-ion batteries is understanding the solid electrolyte interphase (SEI) resulting from a reductive reaction on the anode/electrolyte interface. The presence of the SEI layer affects the transport behavior of the ions and electrons between the anode and electrolyte. Despite the influence on interfacial properties, the formation and evolution mechanism of the SEI layer are unclear owing to their complexity and dynamic nature. Atomistic-scale simulations have promoted the understanding of the reaction mechanism on the anode/electrolyte interface, the formation and evolution of the SEI layer, and their fundamental properties. This Perspective discusses the modeling and interpretations of anode/SEI/electrolyte interfaces through computational methods at the atomic-scale and highlights interfacial modeling techniques for a realistic interface design, which can overcome the limited time and length scale with high accuracy.

Tunable Redox-Active Triazenyl-Carbene Platforms: A New Class of Anolytes for Non-Aqueous Organic Redox Flow Batteries.

Non-aqueous all organic redox flow batteries (NORFBs) are one of the promising options for large-scale renewable energy storage systems owing to their scalability with energy and power along with the affordability. The discovery of new redox-active organic molecules (ROMs) for the anolyte/catholyte would bring them one step closer to the practical application, thus it is highly demanded. Here, we report a new class of ROMs based on cationic triazenyl systems supported by N-heterocyclic carbenes (NHCs) and demonstrate, for the first time, that the triazenyl can serve as a new redox motif for ROMs and could be significantly stabilized for the use in NORFBs by the coupling with NHCs even at radical states. A series of NHC-triazenyl ROM families were successfully synthesized via the reaction of a synthon, N-heterocyclic carbene azido cation, with various Lewis bases including NHCs. Remarkably, it is revealed that NHCs substituted on the triazenyl fragments can serve as a versatile platform for tailoring the electrochemical activity and stability of triazenyl-based compounds, introducing various ROMs exploiting triazenyl redox motif, as demonstrated in the full cell of NORFBs for an anolyte.

Triazenyl Radicals Stabilized by N-Heterocyclic Carbenes.

Notwithstanding the notable progress in the synthesis of N-heterocyclic carbene-stabilized radicals, aminyl radicals, supported by NHCs or otherwise, have been scarcely studied due to synthetic challenges. Triazenyl radical is a particular form of aminyl radical that contains three adjacent nitrogen atoms, and offers intriguing possibilities for unique reactivity and physical properties stemming from expected delocalization of the spin density over the NNN moiety and its conjugated substituents. Here, we report the synthesis and full characterization of the first NHC-stabilized triazenyl radicals, obtained by one-electron reduction of the corresponding triazenyl cations with potassium metal. These radicals reversibly oxidize back to the cations upon treatment with transition metal sources or electrophiles, and abstract H atom from xanthene to form a new N-H bond at the center nitrogen atom. Potential application of the redox couple between triazenyl cation and triazenyl radical was demonstrated as cathode active materials in lithium ion batteries.