Detailed speciation of electrolytes as a function of chemical system and concentration provides the foundation for understanding bulk transport as well as possible decomposition mechanisms. In particular, multivalent electrolytes have shown a strong coupling between anodic stability and solvation structure. Furthermore, solvents that are found to exhibit reasonable stability against alkaline-earth metals generally exhibit low permittivity, which typically increases the complexity of the electrolyte species. To improve our understanding of ionic population and associated transport in these important classes of electrolytes, the speciation of Mg­(TFSI)2 in monoglyme and diglyme systems is studied via a multiscale thermodynamic model using first-principles calculations for ion association and molecular dynamics simulations for dielectric properties. The results are then compared to Raman and dielectric relaxation spectroscopies, which independently confirm the modeling insights. We find that the significant presence of free ions in the low-permittivity glymes in the concentration range from 0.02 to 0.6 M is well-explained by the low-permittivity redissociation hypothesis. Here, salt speciation is largely dictated by long-range electrostatics, which includes permittivity increases due to polar contact ion pairs. The present results suggest that other low-permittivity multivalent electrolytes may also reach high conductivities as a result of redissociation.

Multivalent rechargeable metal batteries offer a safer, more sustainable, and higher energy density alternative to lithium-ion batteries, though several challenges remain. Recent demonstrations of roomtemperature reversible electrodeposition and dissolution of Ca metal indicate that it is possible to stabilize metallic Ca anodes with spontaneously formed solid electrolyte interphases (SEIs). However, further progress toward the goal of an energy-efficient, long cycle-life Ca anode requires correlating interphase identity with electrode performance. In this work, we demonstrate that the SEI formed from calcium borohydride solvated in tetrahydrofuran, an electrolyte that supports reversible Ca deposition, is a compositionally and structurally heterogeneous oxide, sufficiently thin to support Ca 2+ cation transmission while stabilizing Ca from corrosive loss during long-term electrolyte contact. The significant advance demonstrated here is that ionically nonconductive materials, like calcium oxide, can form cation-transmissive interphases in which conductivity can be tailored through control of heterogeneity, providing an approach for stabilizing reactive metal electrodes.

Cu3PS4 nanoparticles are used as a new inorganic hole selective layer (HSL) to fabricate efficient perovskite thin-film solar cells in the inverted device configuration.