Dendrite-free alkali-metal electrodeposition from contact-ion-pair state induced by mixing alkaline earth cation

Alkali metals, such as lithium and sodium, have been expected to be used for rechargeable metal-anode batteries owing to their low electrode potentials and large capacities. However, the well-known fatal problem, “dendritic growth” causing a dangerous short circuit, is faced while charging the batteries. Here, through a comprehensive study with electrochemical experiments, Raman and soft X-ray emission spectroscopies, density-functional-theory calculation, and molecular dynamic simulations, we provide an advanced guideline for electrolyte design in which a mixture of alkaline earth (Mg, Ca, Ba) salts is used to inhibit dendrite growth of alkali metals (Li, Na) during electrodeposition. Especially, focusing on CaTFSA2, as a salient exemplary alkaline-earth-cation additive, we demonstrate that dendrite-free morphology upon alkali-metal electrodeposition can successfully be attained by modifying their solvation structures in the dual-cation electrolyte systems. Adding divalent Ca2+ promotes alkali cation (Li+ or Na+) to form the contact ion pairs (CIPs) with the counter anions, which replaces the solvent-separated ion pairs (SSIPs) commonly existing in single-cation electrolytes. Such CIPs related to alkali cations would separate Ca2+ ions distantly to shield the strong coulomb interaction among the divalent cations. The stronger binding of the CIPs would retard the desolvation kinetics of alkali cations and, consequently, realizes a severely constrained alkali-metal electrodeposition in a reaction-limited process that is required for the dendrite-free morphology. This work provides prospects to construct dual-cation electrolytes for dendrite-free alkali-metal-anode batteries utilizing the concerted interactions between monovalent and multivalent cations.

Wirt-Gast-Komplexe von [bfu.bfu.bfu]: Vorhersage von Ionenselektivitäten mittels quantenchemischer Rechnungen XIII

The CH2–O–C2H4–O–CH2 moieties in Lehn’s cryptand [2.2.2] have been substituted by 2,2′-bifurane groups to get the cryptand [bfu.bfu.bfu]. The ion selectivity of this new cryptand was investigated by DFT calculations (RB3LYP/LANL2DZp, RB3LYP/LACVP*, RBP86/LANL2DZp and RBP86/LACVP*) based on model equations and analysis of the [M ⊂ bfu.bfu.bfu]n+ cryptate structures. The cryptand [bfu.bfu.bfu] is best suited for the alkali cations Na+ and K+, and the alkaline earth cation Sr2+ followed by Ca2+. The cavity of [bfu.bfu.bfu] is thus similar to that in [phen.phen.phen] or [bpy.bpy.bpy]. The selectivity of [bfu.bfu.bfu] is due to the flexibility of the OCCO und CN···NC dihedral angles. The results are independent of the selected DFT methods.

Alkali and Alkaline Earth Cation-Decorated TiO2 Nanotube-Supported Rh Catalysts for Vinyl Acetate Hydroformylation

Alkali and alkaline earth cation-decorated TiO2 nanotube (TNT)-supported rhodium catalysts were synthesized and characterized by inductively-coupled plasma optical emission spectrometer, surface characterization analyzer, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transforming infrared spectrum, respectively. Their catalytic performances were evaluated by the hydroformylation of vinyl acetate. Results showed that both the conversion rate of vinyl acetate and selectivity for aldehyde were improved after Rh/TNTs were modified by alkali or alkali-earth cations. Such improved selectivity for aldehyde might be attributed to the presence of alkali or alkaline earth cations which enhanced CO adsorption, while the high conversion rate of vinyl acetate was likely due to the proper interaction of Lewis acid–base between cations modified TNTs and vinyl acetate.

Alkaline earth cation-mediated photoluminescent complexes of thioflavin T with twisted cucurbit[14]uril

The introduction of alkaline earth metal cations into the tQ[14]–ThT interaction system leds to the precipitation of solid tQ[14]/ThT/AE2+ interaction products, which emitted strong blue fluorescence.