Defining the Reversible Limit of Anionic Redox via Interlayer Li Ordering

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• High-energy sodium-ion batteries require unlocking latent capacity from lattice oxygen.
• Anionic redox chemistry (ARC) is hindered by structural irreversibility and voltage hysteresis.
• Current research focuses on in-plane lithium topology, neglecting long-range interlayer ordering.

Purpose of the Study:

• To define the reversible limit of anionic redox by correlating structure and performance with c-axis lithium ordering.
• To investigate the impact of interlayer lithium stacking on oxygen activity in P2-Na0.7Li0.1Cu0.2Mn0.7O2 (NLCM).
• To establish a protocol for controlling ARC through 3D crystallographic regulation.

Main Methods:

• Utilized P2-Na0.7Li0.1Cu0.2Mn0.7O2 (NLCM) as a model system.
• Employed advanced operando diagnostic analyses to study interlayer Li stacking effects.
• Decoupled interlayer Li stacking from in-plane structures to isolate their influence.

Main Results:

• Turbostratic lithium disorder triggers uncontrolled Li migration, causing excess capacity and degradation.
• A highly ordered lithium stacking framework acts as a structural lock, defining the reversible boundary of ARC.
• Interlayer Li ordering suppressed cation migration and over-activation of anionic capacity, achieving reversible ARC.

Conclusions:

• Ordered interlayer lithium stacking is critical for reversible anionic redox in high-energy sodium-ion batteries.
• This approach significantly reduces voltage hysteresis and improves capacity retention (86% over 200 cycles).
• The study offers a 3D crystallographic regulation strategy to tame ARC, moving beyond 2D design limitations.