Unlocking Reversible Anionic Redox in Layered Oxides via a Cationic-Pair-Mediated Stabilization.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• P2-type layered oxides offer high energy density for sodium-ion batteries (SIBs) via anionic redox.
• Anionic redox in SIBs suffers from oxygen loss and structural degradation, limiting practical application.
• Stabilizing oxygen redox activity is crucial for developing high-performance SIBs.

Purpose of the Study:

• To introduce a cationic-pair-mediated strategy to stabilize anionic redox in P2-type layered oxides.
• To investigate the synergistic effects of Li and Zn cosubstitution on the structure and electrochemical performance of P2-Na_0.78Ni_0.11Li_0.12Zn_0.1Mn_0.67O₂ (NNLZMO).
• To demonstrate a method for concurrently unlocking and stabilizing anionic redox in high-energy layered cathodes.

Main Methods:

• Cosubstitution of Li and Zn into the transition-metal layers of P2-Na_0.78Ni_0.11Mn_0.67O₂ to form NNLZMO.
• Electrochemical characterization including cyclic voltammetry, galvanostatic cycling, and impedance spectroscopy.
• In-situ/ex-situ characterization techniques to analyze structural evolution and phase transitions.

Main Results:

• The Li-Zn cationic pair synergistically activates reversible anionic redox by stabilizing nonbonding O 2p states.
• Structural confinement from the cationic pair suppresses Na⁺/vacancy ordering and prevents irreversible P2-O2 phase transition.
• NNLZMO exhibits a minimal-strain P2-Z phase transition (1.59% volume change), achieving 174.62 mAh g^-1 capacity and 90.8% retention after 100 cycles.

Conclusions:

• Cationic-pair design is an effective strategy for stabilizing anionic redox in P2-type layered oxides.
• The NNLZMO cathode demonstrates enhanced electrochemical performance and structural stability for SIBs.
• This approach paves the way for developing stable, high-energy sodium-ion batteries.