Tailoring Ti Content for Lattice Stable High-Entropy O3-Type Cathode for Sodium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• O3-type layered oxides are key cathode materials for sodium-ion batteries (SIBs).
• Practical SIB application is limited by structural degradation and voltage decay during cycling.
• High-entropy materials offer potential for enhanced stability.

Purpose of the Study:

• To investigate the effect of titanium (Ti) content on the structural stability and electrochemical performance of O3-type high-entropy layered oxides.
• To understand how an electrochemically inactive cation influences framework robustness and reversibility in SIB cathodes.

Main Methods:

• Synthesis and characterization of a series of O3-type high-entropy layered oxides with varying Ti content.
• Electrochemical testing including cycling stability and rate capability measurements.
• In situ/ex-situ X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), and transmission electron microscopy (TEM) analyses.

Main Results:

• The optimized composition, NaNi_0.4Mn_0.3Fe_0.1Ti_0.1Li_0.05Sb_0.05O₂ (HEO-Ti10), demonstrated excellent cycle stability (∼80% capacity retention after 200 cycles) and high rate capability (113 mAh g^-1 at 1.5 A g^-1).
• Moderate Ti incorporation improved lattice robustness and suppressed irreversible phase evolution.
• Ti substitution mitigated instability linked to Mn-site octahedral distortion.

Conclusions:

• Compositional tuning via Ti incorporation is an effective strategy for enhancing the stability of high-entropy layered oxides for SIBs.
• The findings provide insights for designing stable and high-performance cathode materials for practical sodium-ion battery applications.