Molecular crowding electrolytes for high-voltage aqueous batteries

Area of Science:

• Electrochemistry
• Materials Science
• Sustainable Energy

Background:

• Developing safe, high-energy, and sustainable Lithium-ion batteries requires low-cost, eco-friendly aqueous electrolytes with wide voltage windows.
• Current methods using highly concentrated salts improve water stability but pose cost and toxicity issues.
• Molecular crowding in biological systems suppresses water activity via altered hydrogen-bonding structures.

Purpose of the Study:

• To develop a low-cost, eco-friendly aqueous electrolyte with a wide voltage window for sustainable Lithium-ion batteries.
• To utilize the 'molecular crowding' effect to enhance electrolyte performance at lower salt concentrations.
• To demonstrate the viability of this approach in aqueous Lithium-ion battery cells.

Main Methods:

• Employing poly(ethylene glycol) as a molecular crowding agent to decrease water activity in the electrolyte.
• Formulating a low salt concentration (2 m) aqueous electrolyte.
• Constructing and testing aqueous Lithium₄Titanium₅Oxide₁₂/LithiumManganese₂Oxide₄ full cells.
• Utilizing online electrochemical mass spectroscopy to analyze side reactions.

Main Results:

• Achieved a wide electrolyte operation window of 3.2 V with a low salt concentration.
• Demonstrated stable specific energies between 75 and 110 Wh kg^-1 over 300 cycles in full cells.
• Virtually eliminated hydrogen and oxygen evolution reactions, common side reactions in aqueous Lithium-ion batteries.

Conclusions:

• The 'molecular crowding' approach enables high-voltage aqueous electrolytes with reduced salt concentration.
• This method offers a pathway for designing sustainable and cost-effective energy storage solutions.
• The developed electrolyte enhances safety and performance in aqueous Lithium-ion batteries.