Unlocking limited electric double-layer capacity via electrochemically-driven continuous partial desolvations in...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Electrochemical capacitors face limitations due to low electric double-layer storage capacity and narrow operating windows.
• Formation of solid electrolyte interface layers typically restricts performance.

Purpose of the Study:

• To demonstrate electric double-layer adsorption of solvated Na+ in carbon nanopores under a large offset potential.
• To overcome limitations of traditional electrochemical capacitors by enabling enhanced ion adsorption.

Main Methods:

• Utilized a diethylene-glycol-dimethyl-ether electrolyte with a large offset potential (-2.95 V vs. PZC).
• Investigated in-situ partial desolvation of Na+ ions within carbon nanopores.
• Characterized electric double-layer capacitance, capacity, coulombic efficiency, rate capability, and cycling stability.

Main Results:

• Achieved high electric double-layer capacitance (172 F g⁻¹) and capacity (508 C g⁻¹).
• Demonstrated high initial coulombic efficiency (92.2%) and excellent rate capability.
• Developed sodium-ion capacitor pouch cells with high specific energy (40 Wh kg⁻¹) and long cycle life (30,000 cycles).

Conclusions:

• Enlarged offset potential drives ion desolvation, significantly boosting electric double-layer charge storage.
• The developed sodium-ion capacitors offer high performance without pretreatment, suitable for industrial scale-up.
• This approach enables redesign of high-performance sodium-ion capacitors with improved energy density and cycling stability.