Reversible Electrochemical Anionic Redox in Rechargeable Multivalent-Ion Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Rechargeable multivalent-ion batteries offer high capacity but lack suitable cathode materials for efficient ion intercalation.
• Crystalline chevrel phases are rare cathode materials that can reversibly intercalate multivalent cations.
• Lack of design rules hinders the development of stable multivalent-ion intercalation electrodes.

Purpose of the Study:

• To elucidate the charge storage mechanism in chevrel phase electrodes during multivalent cation intercalation.
• To identify design principles for novel intercalation electrodes facilitating multivalent cation insertion.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) spectroscopy
• Synchrotron X-ray absorption near edge structure (XANES) measurements
• Operando synchrotron X-ray diffraction
• Density functional theory (DFT) calculations

Main Results:

• Electrons are selectively transferred to the anionic chalcogen framework upon cation intercalation.
• Transition metal (Mo) octahedra remain redox inactive during the process.
• A reversible electrochemical anionic redox mechanism occurs without chemical bond disruption.

Conclusions:

• The charge storage in chevrel phases involves reversible anionic redox, distinct from typical transition metal-based electrodes.
• Understanding this mechanism provides design principles for advanced multivalent-ion battery cathodes.
• This work paves the way for developing new intercalation electrodes for efficient multivalent cation storage.