An official website of the United States government
Abstract Insights into structure‐conductivity mechanisms are investigated for a series of six (dinitrile)2LiPF6 molecular crystals with varied alkyl chain lengths, N≡C─(CH2)n─C≡N, n = 2, 3, 4, 5, 6, and 2Me‐glutaronitrile. The molecular crystals have separate Li+ and channels, with the Li+ions weakly coordinated by four ─C≡N groups. The following correlations are observed: i) shorter Li+⋯ Li+ hopping distances (5.72–8.08 Å) increase ionic conductivity (3.1 × 10−4–0.15 × 10−4 S cm−1 at 25 °C) for all (dinitrile)2LiPF6; ii) when there are unrestricted anion channels, the lithium ion transference number increases ( = 0.39–0.62) as the void volume (565–250 Å3) and Li+⋯ Li+ hopping distance (7.15–5.72 Å) decrease, since a greater fraction of the charge is contributed by the Li+ions; this correlates with n= 2, 4, 5, 6; iii) the exceptions are Gln (n = 3) and 2Me‐Gln, where there are restricted channels for anion migration, and in this case: iv) conductivity decreases (0.57–0.15 × 10−4 S cm−1 at 25 °C), since contributions to the conductivity from anion migration decrease, but v) increases (0.64–0.7) since a greater fraction of the charge is carried by the Li+ ions.
more »
« less
Reduction of π‐Expanded Cyclooctatetraene with Lithium: Stabilization of the Tetra‐Anion through Internal Li + Coordination
Abstract The chemical reduction of a π‐expanded polycyclic framework comprising a cyclooctatetraene moiety, octaphenyltetrabenzocyclooctatetraene, with lithium metal readily affords the corresponding tetra‐anion instead of the expected aromatic dianion. As revealed by X‐ray crystallography, the highly contorted tetra‐anion is stabilized by coordination of two internally bound Li+, while two external cations remain solvent separated. The variable‐temperature7Li NMR spectra in THF confirm the presence of three types of Li+ions and clearly differentiate internal binding, consistent with the crystal structure. Density‐functional theory calculations suggest that the formation of the highly charged tetra‐reduced carbanion is stabilized through Li+coordination under the applied experimental conditions.
more »
« less
- PAR ID:
- 10236773
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 60
- Issue:
- 7
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 3510-3514
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract New acceptor‐type graphite intercalation compounds (GICs) offer candidates of cathode materials for dual‐ion batteries (DIBs), where superhalides represent the emerging anion charge carriers for such batteries. Here, the reversible insertion of [LiCl2]−into graphite from an aqueous deep eutectic solvent electrolyte of 20mLiCl+20mcholine chloride is reported. [LiCl2]−is the primary anion species in this electrolyte as revealed by the femtosecond stimulated Raman spectroscopy results, particularly through the rarely observed H–O–H bending mode. The insertion of Li–Cl anionic species is suggested by7Li magic angle spinning nuclear magnetic resonance results that describe a unique chemical environment of Li+ions with electron donors around.2H nuclear magnetic resonance results suggest that water molecules are co‐inserted into graphite. Density functional theory calculations reveal that the anionic insertion of hydrated [LiCl2]−takes place at a lower potential, being more favorable. X‐ray diffraction and the Raman results show that the insertion of [LiCl2]−creates turbostratic structure in graphite instead of forming long‐range ordered GICs. The storage of [LiCl2]−in graphite as a cathode for DIBs offers a capacity of 114 mAh g−1that is stable over 440 cycles.more » « less
-
Abstract Covalent organic frameworks linked by carbon‐carbon double bonds (C=C COFs) are an emerging class of crystalline, porous, and conjugated polymeric materials with potential applications in organic electronics, photocatalysis, and energy storage. Despite the rapidly growing interest in sp2carbon‐conjugated COFs, only a small number of closely related condensation reactions have been successfully employed for their synthesis to date. Herein, we report the first example of a C=C COF, CORN‐COF‐1 (CORN=Cornell University), prepared byN‐heterocyclic carbene (NHC) dimerization. In‐depth characterization reveals that CORN‐COF‐1 possesses a two‐dimensional layered structure and hexagonal guest‐accessible pores decorated with a high density of strongly reducing tetraazafulvalene linkages. Exposure of CORN‐COF‐1 to tetracyanoethylene (TCNE,E1/2=0.13 V and −0.87 V vs. SCE) oxidizes the COF and encapsulates the radical anion TCNE⋅−and the dianion TCNE2−as guest molecules, as confirmed by spectroscopic and magnetic analysis. Notably, the reactive TCNE⋅−radical anion, which generally dimerizes in the solid state, is uniquely stabilized within the pores of CORN‐COF‐1. Overall, our findings broaden the toolbox of reactions available for the synthesis of redox‐active C=C COFs, paving the way for the design of novel materials.more » « less
-
Anionic forms of a macrocyclic cyclophane were crystallized by treating the neutral hydrocarbon with alkali metals (Li, Na and K). The di-anions show decreased bond-length alternation, consistent with global aromaticity, whereas the anti-aromatic tetra-anion has a low-symmetry geometry.more » « less
-
Abstract The concept of employing highly concentrated electrolytes has been widely incorporated into electrolyte design, due to their enhanced Li‐metal passivation and oxidative stability compared to their diluted counterparts. However, issues such as high viscosity and sub‐optimal wettability, compromise their suitability for commercialization. In this study, we present a highly concentrated dimethyl ether‐based electrolyte that appears as a liquid phase at ambient conditions via Li+‐ solvents ion‐dipole interactions (Coulombic condensation). Unlike conventional high salt concentration ether‐based electrolytes, it demonstrates enhanced transport properties and fluidity. The anion‐rich solvation structure also contributes to the formation of a LiF‐rich salt‐derived solid electrolyte interphase, facilitating stable Li metal cycling for over 1000 cycles at 0.5 mA cm−2, 1 mAh cm−2condition. When combined with a sulfurized polyacrylonitrile (SPAN) electrode, the electrolyte effectively reduces the polysulfide shuttling effect and ensures stable performance across a range of charging currents, up to 6 mA cm−2. This research underscores a promising strategy for developing an anion‐rich, high concentration ether electrolyte with decreased viscosity, which supports a Li metal anode with exceptional temperature durability and rapid charging capabilities.more » « less
