Empowering Reversible Anionic Redox in Sodium Layered Oxide Cathodes via Ionic Impedance Matching Interphase

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anionic redox reactions (ARR) in sodium manganese-based cathodes offer high energy density but face interfacial instability and degradation at high voltages.
• Interfacial instability is a major challenge limiting the performance and cycle life of sodium-ion batteries.

Purpose of the Study:

• To design and implement an ionic impedance matching interphase to enhance the stability of sodium manganese-based layered oxide cathodes.
• To mitigate interfacial degradation and improve electrochemical performance by harmonizing mechanical compatibility and ionic transport.

Main Methods:

• Formation of a composite interphase via thermally driven conversion of NaTi2(PO4)3 on P2-Na5/6Li1/4Mn3/4O2.
• Characterization of the interphase architecture, including outer Na3PO4 and inner Ti-rich spinel-like layers.
• Investigation of the interphase's role in stabilizing interfacial chemistry, suppressing gas evolution, and mitigating Jahn-Teller distortion.

Main Results:

• A stable interphase comprising Na3PO4 and a Ti-rich spinel-like layer was successfully formed, exhibiting strong lattice compatibility and robust Ti-O-P linkages.
• The interphase effectively shielded reactive oxygen species, suppressed gas evolution, and introduced lattice-permeated Ti doping, reinforcing Ti-O covalency.
• Achieved high discharge capacity (~230 mAh g-1) and low voltage decay (<0.05 V) over extended cycling, demonstrating significantly improved stability.

Conclusions:

• The ionic impedance matching interphase provides an effective strategy for stabilizing anionic redox chemistry in high-energy sodium-ion batteries.
• This work offers deep mechanistic insights into interfacial regulation, paving the way for advanced sodium-ion battery development.
• The developed interphase successfully mitigates degradation pathways, enabling high performance and long cycle life.