Structural Rearrangements of a Cobalt-Free Lithium-Rich Layered Oxide Cathode during Formation.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-state Chemistry

Background:

• First-cycle formation in lithium-rich layered oxide (LRLO) cathode materials is critical for interphase consolidation and long-term cyclability.
• The specific structural and compositional changes during formation are material-dependent and not well understood for Co-free, Ni-poor LRLOs.

Purpose of the Study:

• To analyze the formation processes in a representative Co-free, Ni-poor LRLO (Li _1.28Ni _0.15Mn _0.57O ₂) to understand its activation pathway.
• To elucidate the structural and lattice changes that enable stable cycling in this important class of cathode materials.

Main Methods:

• Combined electrochemistry, *operando* mass spectrometry, X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS).
• Density functional theory (DFT) simulations were employed to complement experimental findings.

Main Results:

• Activation significantly compresses the *c*-axis layer spacing and enhances reversible structural breathing.
• High capacity (~250 mAh g^-1) arises from coupled Ni and O redox processes, with O-redox occurring across the entire anionic sublattice.
• Irreversible structural evolution of MnO ₆ octahedra, driven by sequential Ni and O redox, enables superior electrochemical performance without detrimental oxygen evolution.

Conclusions:

• A distinct activation pathway for Co-free, Ni-poor LRLOs has been identified, characterized by significant structural and lattice changes.
• This pathway facilitates reversible O-redox and enables high capacity and stability, crucial for next-generation batteries.
• The findings provide guidance for designing advanced, sustainable cathode materials with improved electrochemical properties.