Mg Substitution Induced TM/Vacancy Disordering and Enhanced Structural Stability in Layered Oxide Cathode Materials

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anionic redox in cathode materials boosts capacity for sodium-ion batteries (SIBs).
• Na2Mn3O7 shows promise but suffers from phase transitions and potential decay at low potentials.
• Ordered transition metal (TM) vacancies in Na2Mn3O7 enable oxygen redox but lead to instability.

Purpose of the Study:

• To enhance the structural stability and electrochemical performance of Na2Mn3O7 for SIBs.
• To investigate the effect of magnesium (Mg) doping on the anionic redox and structural integrity.
• To explore the relationship between atomic ordering and electrochemical properties in cathode materials.

Main Methods:

• Magnesium (Mg) was doped into the transition metal vacancies of Na2Mn3O7.
• The resulting disordered Mn/Mg/□ arrangement was analyzed for its impact on oxygen redox and phase transitions.
• Electrochemical cycling performance and sodium-ion diffusivity were evaluated in the voltage range of 1.5-4.5 V.

Main Results:

• Mg substitution created a disordered TM layer, suppressing oxygen oxidation and mitigating low-potential phase transitions.
• The disordered structure inhibited the formation of dissolvable Mn2+ ions, improving structural stability.
• Na0.49Mn0.86Mg0.06□0.08O2 exhibited enhanced Na+ diffusivity and superior rate performance compared to the pristine material.

Conclusions:

• Disordering the TM layer via Mg doping significantly improves the cycling stability and electrochemical performance of Na2Mn3O7 cathodes.
• The study highlights the critical role of atomic arrangement in controlling anionic redox and battery performance.
• This work offers insights into balancing anionic and cationic redox for developing high-energy SIB cathode materials.