Breaking the Conversion Limit in an Intercalation-Type Cathode by Loosening Aqueous Cation Coordination

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Intercalation cathodes are standard in aqueous multivalent ion storage.
• Conversion reactions offer higher theoretical capacities but compromise stability and kinetics.
• A significant performance trade-off exists between intercalation and conversion mechanisms.

Purpose of the Study:

• To extend intercalation-type electrodes into the conversion regime without sacrificing performance.
• To overcome the longstanding trade-off between capacity, stability, and kinetics in aqueous ion storage.
• To enhance the energy density of aqueous batteries through novel electrode mechanisms.

Main Methods:

• Utilized dilute aqueous systems with Bi2Se3 electrodes to loosen cation coordination.
• Employed operando synchrotron X-ray diffraction, first-principle calculations, and ex situ spectroscopy (XAS, EM).
• Investigated the role of hydrophobic perchlorate in optimizing solvation and charge transfer.

Main Results:

• Achieved a twofold capacity increase to 417.6 mAh g−1 by enabling conversion reactions in Bi2Se3.
• Demonstrated excellent cycling stability (20,000 cycles, 0.013‰ decay) and rate capability (314.6 mAh g−1 at 30 A g−1).
• Identified optimized cation coordination and charge transfer as key to enhanced performance and unique intercalation-conversion mechanisms.

Conclusions:

• Loosening cation coordination unexpectedly enables intercalation electrodes to enter the conversion regime.
• Hydrophobic perchlorate optimizes interfacial properties, reducing barriers and enhancing potential for reversible conversion.
• This approach offers high ion mobility, low-temperature performance, and robust quasi-solid-state operation, advancing aqueous battery technology.