Depth-dependent valence stratification driven by oxygen redox in lithium-rich layered oxide

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium-rich nickel-manganese-cobalt (LirNMC) layered materials offer high energy density for lithium-ion batteries.
• These materials exhibit voltage decay during cycling, hindering practical application.
• Understanding particle-level structure and chemistry is crucial for improving performance.

Purpose of the Study:

• To investigate the 3D morphology, composition, and chemical states of LirNMC particles.
• To elucidate the mechanisms behind voltage decay in LirNMC cathodes.
• To explore strategies for mitigating performance degradation.

Main Methods:

• 3D morphological, compositional, and chemical analysis of Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ particles.
• Investigation of transition metal valence states and their depth dependency.
• Correlation of particle morphology with chemical variations.

Main Results:

• Particle composition was generally uniform, but charging induced depth-dependent transition metal valence.
• Valence stratification was observed, likely linked to Mn-associated oxygen redox activity.
• A structural-chemical interplay was identified, influenced by core-multi-shell morphology.

Conclusions:

• Depth-dependent chemistry and valence stratification are key factors in LirNMC performance.
• Oxygen redox activity, particularly involving Mn, plays a significant role.
• Introducing a chemical gradient may help address oxygen-loss-induced voltage fade in LirNMC materials.