Transition metal vacancy and position engineering enables reversible anionic redox reaction for sodium storage

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Anionic redox reactions in layered transition metal oxides can significantly increase energy storage capacity.
• However, challenges include irreversible oxygen release and structural instability at high voltages, limiting practical applications.

Purpose of the Study:

• To develop a novel doping strategy to enhance the reversibility of anionic redox reactions and improve the structural stability of layered oxides for sodium storage.
• To investigate the effects of dual Mg ion and vacancy doping, along with partial transition metal ion migration, on electrochemical performance.

Main Methods:

• Synthesized a novel layered oxide material, Na 0.67 Mn 0.011 [Mg 0.1 □ 0.07 Mn 0.83 ]O 2 , using a dual doping approach.
• Characterized the material's structure and electrochemical properties, focusing on anionic redox behavior and cycling stability.
• Utilized theoretical insights to explain the roles of Mg ions, vacancies, and pinned Mn ions in enhancing performance.

Main Results:

• The Mg ion and vacancy dual doping strategy successfully created nonbonding O 2p orbitals, promoting high oxygen redox capacity.
• Partial Mn ion migration to Na sites acted as "rivets," effectively suppressing slab gliding and crack formation during deep sodiation.
• The modified electrode material exhibited enhanced discharge capacity and improved cyclability compared to undoped counterparts.

Conclusions:

• The developed doping strategy offers a promising pathway for designing stable layered oxide electrodes with highly reversible anionic redox reactions for advanced sodium storage.
• This work provides fundamental insights into controlling anionic redox activity and structural integrity in layered materials through strategic ion and vacancy doping.