Solvate electrolytes for Li and Na batteries: structures, transport properties, and electrochemistry

Polar solvents dissolve Li and Na salts at high concentrations and are used as electrolyte solutions for batteries. The solvents interact strongly with the alkali metal cations to form complexes in the solution. The activity (concentration) of the uncoordinated solvent decreases as the salt concentration is increased. At extremely high salt concentrations, all the solvent molecules are involved in the coordination of the ions and form the solvates of the salts. In this article, we review the structures, transport properties, and electrochemistry of Li/Na salt solvates. In molten solvates, the activity of the uncoordinated solvent is negligible; this is the main origin of their peculiar characteristics, such as high thermal stability, wide electrochemical window, and unique ion transport. In addition, the solvent activity greatly influences the electrochemical reactions in Li/Na batteries. We highlight the attractive features of molten solvates as promising electrolytes for next-generation batteries.

Automated summary

Polar solvents can dissolve Li and Na salts at high concentrations, forming complexes in the solution. The activity of uncoordinated solvent decreases with increasing salt concentration, eventually leading to the formation of solvates. Molten solvates exhibit unique characteristics such as high thermal stability and wide electrochemical window due to negligible activity of uncoordinated solvent. Solvent activity greatly influences electrochemical reactions in Li/Na batteries, highlighting the potential of molten solvates as promising electrolytes for next-generation batteries.