Cationic-potential tuned biphasic layered cathodes for stable desodiation/sodiation

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium layered oxides face challenges: P2 structures exhibit deep-desodiation instability, while O3 structures show sluggish kinetics.
• Designing P2/O3 biphasic materials offers a promising approach to combine the advantages of both structures for improved sodium-ion battery performance.

Purpose of the Study:

• To elucidate the formation mechanism of P2/O3 biphasic structures in sodium layered oxides.
• To synthesize and characterize novel P2/O3 biphasic materials with enhanced electrochemical properties.
• To understand the sodium storage mechanism in these advanced cathode materials.

Main Methods:

• Theoretical simulations and various spectroscopies were employed to investigate the formation mechanism.
• Solid-state reactions were controlled by constraining temperature-driven ion diffusion.
• Synchrotron-based diffraction and X-ray absorption spectroscopy were utilized for in-depth analysis.

Main Results:

• The study identified internal cationic potential heterogeneity as the origin of P2/O3 biphasic structures.
• A novel P2/O3 biphasic Na_0.7Ni_0.2Cu_0.1Fe_0.2Mn_0.5O_2-δ material was successfully synthesized.
• The biphasic material demonstrated significantly improved rate capabilities (62 mAh g^-1 at 2.4 A g^-1) and cycling stability (84% capacity retention after 500 cycles) compared to single-phase analogues.

Conclusions:

• Controlling ion diffusion during synthesis is key to realizing P2/O3 biphasic structures.
• The developed P2/O3 biphasic layered oxides represent a significant advancement for sodium-ion battery cathodes.
• This research provides critical insights for the rational design of high-performance sodium-ion battery materials.