High-Energy Aqueous Sodium-Ion Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Water-in-salt electrolytes (WISE) offer an expanded electrochemical stability window (ESW) for aqueous electrolytes.
• Limitations of current WISE in aqueous sodium-ion batteries (ASIBs) include high cathodic potential and prohibitive costs.
• Existing WISE systems struggle to accommodate high-capacity anodes due to insufficient cathodic potential.

Purpose of the Study:

• To design a cost-effective bi-salts WISE with an extended electrochemical stability window for ASIBs.
• To investigate the electrolyte's performance with high-capacity anodes.
• To address the limitations of current WISE in terms of cost and cathodic potential.

Main Methods:

• Development of a 19 mol kg^-1 bi-salts WISE comprising NaClO₄ and NaOTF in water.
• Electrochemical characterization to determine the ESW and interfacial properties.
• Fabrication and testing of a Na₃ V₂ (PO₄ )₃ ∥Na₃ V₂ (PO₄ )₃ full cell.

Main Results:

• The designed WISE exhibits a wide ESW of 2.8 V, with anodic potential extended to 4.4 V and cathodic potential to 1.6 V.
• A NaF-Na₂ O-NaOH solid electrolyte interphase (SEI) is formed on the anode, enhancing stability.
• The full cell achieved an energy density of 70 Wh kg^-1 at 1C with 87.5% capacity retention after 100 cycles.

Conclusions:

• The low-cost bi-salts WISE effectively expands the ESW for ASIBs.
• The electrolyte demonstrates suitability for high-capacity anodes, enabling improved battery performance.
• This work presents a viable pathway towards practical and high-performance aqueous sodium-ion batteries.