Biphasic P2/O3-Na_2/3Li_0.18Mn_0.8Fe_0.2O₂: a structural investigation

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• P2/O3 layered oxides show promise for sodium-ion batteries due to synergistic phase effects.
• Understanding phase interactions and ion occupancy is crucial for optimizing cathode performance.

Purpose of the Study:

• To investigate the structural behavior of biphasic P2/O3-Na2/3Li0.18Mn0.8Fe0.2O2.
• To determine lithium site preference in the O3 phase.
• To analyze the structural evolution during electrochemical cycling.

Main Methods:

• Neutron diffraction for atomic site occupancy.
• Operando X-ray diffraction for real-time structural analysis during cycling.
• Synthesis and characterization of biphasic P2/O3 cathode material.

Main Results:

• Neutron diffraction confirmed full lithium occupancy of the O3 alkali metal site.
• Operando X-ray diffraction showed no formation of O2, OP4, or Z phases at the charged state.
• The P2/O3 composite electrode exhibits structural stability during cycling.

Conclusions:

• Lithium exhibits a strong preference for O3 sites in this biphasic system.
• The absence of detrimental phase transitions highlights the material's robustness.
• Utilizing multiple phases in layered cathode materials is a viable strategy for high-performance sodium-ion batteries.