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.

Structural distortions of orthorhombic RFeO3 and RMnO3

We will address in detail the structural distortions responsible for the symmetry lowering of the ideal cubic Pm-3m perovskite to the orthorhombic Pnma structure of RFeO3 and RMnO3 (R = trivalent rare-earth cation), important to the stabilization of the different magnetic and multiferroic phases in these materials. We will also show how the Amplimodes tool of Bilbao Crystallographic Server is useful in quantifying these distortions and establish which phonons can be used as probes of both the octahedra tilting and deformation.

Crystal structure of K3EuSi2O7

As a part of the research of the flux technique for growing alkali rare-earth elements (REE) containing silicates, tripotassium europium disilicate, K3EuSi2O7, has been synthesized and characterized by single-crystal X-ray diffraction. It crystallizes in the space group P63/mcm. In the crystal structure of the title compound, one part of the Eu cations are in a slightly distorted octahedral coordination and the other part are in an ideal trigonal prismatic coordination environment. The disilicate Si2O7 groups connect four EuO6 octahedra and one EuO6 trigonal prism. Three differently coordinated potassium cations are located between them. Silicates containing the larger rare earth elements usually crystallize in a structure that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment.

COMPOSTOSORGANOMETÁLICOS DEESTANHO(II) –ESTANILAS DEALGUNSMETAIS REPRESENTATIVOS

ORGANOMETALLICCOMPOUNDSOFTIN(II) –SOMEMAINGROUPMETALSTANNYLS.This paper aimsto summarise some chemical information aboutselected main group metalstannyl compounds. The number of these compoundsin the literature are much fewer than those with transition metal cations. Most papersreport details ofstannyls containing Li(I), Na(I) and K(I),such assynthetic routes, spectroscopic results and their molecular structures. This review comprises not only information of stannyls containing these cations, but also some alkaline-earth species containingMg(II),Ca(II),Sr(II),Ba(II), aswell asSn(II).In some compounds,the alkaline or alkaline earth cation is connected to the stannylfragmentthrough aSn –Mbond, evidenced byX-ray crystallographic data or by solutionorsolid-state 119SnNMRexperiments.The introduction part ofthe papersummarizesthe chemical aspects ofthese compounds and their importance in the organometallic chemistry ofSn(II) as a research area.The second part ofthisreviewis dedicated to a broad discussion of the syntheses and structural aspects ofsomeLi(I),Na(I) andK(I) derivatives.The structure ofsome stannyl compounds ofMg(II),Ca(II), Sr(II),Ba(II) are displayed in the third part ofthis paper.Two rare examples of Sn(II)-based stannyl derivatives are shown in the final part ofthe review.Thisreview also highlights how important it isto correlate X-ray crystallographic data with those obtained by solution- or solid-state 119Sn-NMRexperimentsin orderto determine the degree of covalence in the Sn –Mbond.

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.