Given the prior success in developing lithium batteries for similar purposes, many of the same types of solvent molecules and salt pairings have been investigated as electrolytes in sodium-ion and sodium−oxygen systems. Of these candidates, ether-containing electrolytes have emerged as a promising material as a result of their electrochemical stability and utility in tuning the pertinent electrochemistry. The ability for ethers to chelate metal ions provides a unique feature to ion solvation structure; however its role in changing the association of ions in solution has not been fully explored. By using computational simulations validated by FTIR and NMR spectroscopy, detailed descriptions of the changes to solvation structure as a result of chelation and concentration were investigated for a series of ethers (monoglyme to tetraglyme). From these simulations it can clearly be seen that with increasing chelation, ion association is diminished in a nonlinear fashion. For a monoglyme solvent, sodiums are entirely coordinated by triflates in solution, even at low concentrations. In contrast, tetraglymes retain a significant solvent separation of sodium cations from triflate anions even at high concentrations. The former implies that the utility of monoglyme and diglyme solvents for sodium−air batteries in specific is likely linked to their favoring ion association, while the poor performance of tetraglyme is a result of its excessive binding to sodium. Finally, triglyme was shown to produce anomalous behavior as a result of a mismatch between sodium coordination and steric interactions.

High concentration lithium electrolytes have been found to be good candidates for high energy density and high voltage lithium batteries. Recent studies have shown that limiting the free solvent molecules in the electrolytes prevents the degradation of the battery electrodes. However, the molecular level knowledge of the structure and dynamics of such an electrolyte system is limited, especially for electrolytes based on typical organic carbonates. In this article, the interactions and motions involved in lithium bis(trifluoromethanesulfonyl)imide in carbonyl-containing solvents are investigated using linear and timeresolved vibrational spectroscopies and computational methods. Our results suggest that the overall structure and the speciation of the three high concentration electrolytes are similar. However, the cyclic carbonate-based electrolyte presents an additional interaction as a result of dimer formation. Time-resolved studies reveal similar and fast dynamics for the structural motions of solvent molecules in electrolytes composed of linear molecules, while the electrolyte made of cyclic solvent molecules shows slower structural changes as a result of the dimer formation. Additionally, a picosecond time scale process is observed and assigned to the coordination and decoordination of solvent molecules from a lithium-ion solvation shell. This process of solvent exchange is found to be directly correlated to the making and breaking of structures between the lithium-ion and the anion and, consequently, to the conduction mechanism. Overall, our data show that the molecular structure of the solvent does not significantly affect the speciation and distribution of the lithium-ion solvation shells. However, the presence of dimerization between solvent molecules of two neighboring lithium-ions appears to produce a microscopic ordering that it is manifested macroscopically in properties of the electrolyte, such as its viscosity.

New highly concentrated electrolytes based on ether solvents were developed for sodium electrochemical cells. The investigated electrolytes use sodium triflate and glycol diether oligomers of different length to form the electrolyte. These electrolytes present conductivities that increase as a function of concentration even when the electrolyte is composed of a majority of ion pairs and aggregates. Correlation analysis between the electrolyte speciation and conductivity suggests the presence of two distinct mechanisms of charge transport, namely a traditional vehicular mechanism based on the diffusion of free ions and a hopping mechanism involving the making and breaking of ion-pairs and/or aggregates. The former mechanism represents the charge transport of glyme with 3 or 4 units, while the latter is observed in electrolytes composed of short chains, i.e., 1 or 2 units. The proposed mechanism of transport is corroborated via molecular dynamics simulations. In addition, our experiments demonstrate that the high concentration of the sodium salt not only increases the overall conductivity of the electrolyte but also does not affect its electrochemical window.

Hydrogen bonds (H bonds) play a major role in defining the structure and properties of many substances, as well as phenomena and processes. Traditional H bonds are ubiquitous in nature, yet the demonstration of weak H bonds that occur between a highly polarized C−H group and an electron‐rich oxygen atom, has proven elusive. Detailed here are linear and nonlinear IR spectroscopy experiments that reveal the presence of H bonds between the chloroform C−H group and an amide carbonyl oxygen atom in solution at room temperature. Evidence is provided for an amide solvation shell featuring two clearly distinguishable chloroform arrangements that undergo chemical exchange with a time scale of about 2 ps. Furthermore, the enthalpy of breaking the hydrogen bond is found to be 6–20 kJ mol−1. Ab‐initio computations support the findings of two distinct solvation shells formed by three chloroform molecules, where one thermally undergoes hydrogen‐bond making and breaking.

The structure of different sodium–glyme–thiocyanate complexes has been studied by linear and time resolved vibrational spectroscopies.