Achieving Zero Phase Transition in P2-Type Layered Oxides via Targeted Chemical Design for Zero-Strain Sodium...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• P2-type layered oxide cathodes are crucial for sodium-ion batteries (SIBs) due to fast sodium ion kinetics.
• Phase transitions in these cathodes, like P2-to-O2, degrade performance and structural integrity.

Purpose of the Study:

• To design a stage-specific cathode material that suppresses phase transitions in P2-type layered oxides.
• To address the O^2- repulsion, the root cause of phase transitions during desodiation.

Main Methods:

• Chemical design of a novel cathode material: Na_0.67Ni_0.05Fe_0.05Ti_0.05Cu_0.2Mn_0.65O₂ (NFTCM).
• Utilized in situ X-ray diffraction to observe phase transition behavior.
• Employed operando neutron diffraction to analyze the oxygen framework stability.

Main Results:

• The NFTCM cathode achieved a record Na-layer spacing (3.67 Å) with minimized O^2- repulsion.
• Demonstrated true zero-phase-transition behavior with minimal volume change (0.062%) during cycling.
• Exhibited excellent rate capability (121 mAh/g at 10C) and long-term cycling stability (93.7% capacity retention after 600 cycles).

Conclusions:

• The stage-specific chemical design effectively eliminates phase transitions in P2 cathodes.
• The zero-strain mechanism significantly enhances the structural stability and electrochemical performance of SIBs.
• A robust oxygen framework, enabled by suppressed phase transitions, is key to stable ion storage in layered oxides.