Water-In-Salt Electrolyte

A water‑in‑salt electrolyte is a liquid medium in which the concentration of dissolved salt approaches or exceeds the point at which there are essentially no “free” water molecules left. In this regime, most of the water molecules are coordinated to cations, forming solvation shells that dramatically reduce the ability of water to participate in side reactions such as hydrogen evolution. Because the solvent’s reactivity is suppressed, the electrolyte can tolerate higher electrode potentials than a conventional dilute aqueous solution.

The main appeal of water‑in‑salt electrolytes lies in their combination of safety and performance. The high ionic strength delivers good conductivity while the limited availability of free water expands the electrochemical stability window, allowing aqueous batteries to operate at voltages that were previously only reachable with flammable organic solvents. This opens a pathway toward low‑cost, non‑flammable energy storage devices that can be charged rapidly without sacrificing cycle life.

You will encounter water‑in‑salt electrolytes wherever researchers are trying to bridge the gap between traditional aqueous cells and high‑energy organic batteries: in experimental lithium‑ion and sodium‑ion aqueous chemistries, in hybrid supercapacitor designs, and increasingly in prototypes for grid‑scale storage where safety and cost are paramount. The concept also informs broader discussions about solvent design, showing how manipulating solvation structure can tune the fundamental limits of electrochemical reactions.