Spontaneous polyiodide formation by unbalancing of charge in room-temperature ionic liquid-lithium salt solutions

New Redox Chemistries of Halogens in Aqueous Batteries

Halogen-based redox-active materials represent an important class of materials in aqueous electrochemistry. The existence of versatile halogen species and their rich bonding coordination create great flexibility in designing new redox couples. Novel redox reaction mechanisms and electrochemical reversibility can be unlocked in specifically configurated electrolyte environments and electrodes. In this review, the halogen-based redox couples and their appealing redox chemistries in aqueous batteries, including redox flow batteries and traditional static batteries that have been studied in recent years, are discussed. New aqueous electrochemistry provides hope to outperform the state-of-the-art materials and systems that are facing resources and performance limitation, and to enrich the existing battery chemistries.

Peculiar High-Pressure Phase Behavior of 1-Butyl-3-methylimidazolium Iodide

We investigated the stability of the liquid phase of 1-butyl-3-methylimidazolium iodide (hereafter abbreviated as [C₄mim][I]) up to 16.7 GPa at room temperature. We observed a peculiar phase transition behavior in the [C₄mim][I] sample. In particular, a glassy state was formed at ∼1.3 GPa; however, the reddish-brown precipitate was formed probably due to concentrated I₃^- or I₂^- species that were formed above 12 GPa; [C₄mim][I] showed a pressure-induced partial crystallization from the glassy state. We concluded that the conformation of [C₄mim]⁺ is essential in iterative modulation to control the environmental formation of iodide precipitate.

Lithium-triggered spontaneous formation of polyiodides in room-temperature ionic liquid-alcohol solutions

In this study, the effect of alcohol on polyiodide formation in room-temperature ionic liquid (RTIL) was examined by time evolutions of Raman spectra in the low-frequency region and by color changes of the sample. The RTIL was 1-methyl-3-propylimidazolium iodide, [C₃mim][I]. Polyiodides develop in [C₃mim][I]‑lithium salt-ethanol solutions (Abe et al., Chem. Phys. 502 (2018) 72.). Without the external addition of iodine or without an external electric field, the irreversible transformation from I^- to I₃^- indicates that charge unbalancing was promoted by lithium ion. Polyiodide formations were not induced by sodium or potassium ions. Strong alcohol effects were observed directly by the time-dependent Raman bands in the low-frequency region.