Strengthening Aqueous Electrolytes without Strengthening Water

Area of Science:

• Electrochemistry
• Materials Science
• Physical Chemistry

Background:

• Aqueous electrolytes typically have limited electrochemical stability.
• Developing stable electrolytes is crucial for advanced battery technologies.

Purpose of the Study:

• To investigate the electrochemical stability of eutectic aqueous solutions at low temperatures.
• To understand the underlying mechanisms of enhanced stability.
• To demonstrate the application of such electrolytes in aqueous lithium-ion batteries.

Main Methods:

• Experimental characterization of a eutectic LiCl-H3PO4 aqueous solution cooled to -78°C.
• Computational simulations (e.g., molecular dynamics) to analyze ion solvation and water structure.
• Fabrication and testing of an aqueous Li-ion battery using LiMn2O4 cathode and CuSe anode.

Main Results:

• The eutectic aqueous solution exhibited a significantly widened electrochemical stability window at -78°C.
• Cooling led to reduced Li+ hydration, Li+-Cl- pairing, ice-like water clusters, and strengthened H···Cl- bonds.
• A novel mechanism for low-temperature water inertness was proposed, involving unfavorable solvation of OH- and H+.
• An aqueous Li-ion battery demonstrated a high energy density of 109 Wh/kg.

Conclusions:

• Low-temperature eutectic aqueous solutions offer enhanced electrochemical stability.
• The stability mechanism involves specific ion-water interactions rather than O-H bond stiffening.
• These findings open possibilities for robust aqueous batteries in extreme environments.