Sodium Layered/Tunnel Intergrowth Oxide Cathodes: Formation Process, Interlocking Chemistry, and Electrochemical...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Manganese-based layered oxides are promising cathode materials for sodium-ion batteries (SIBs) due to their cost-effectiveness and high theoretical capacities.
• The biphasic intergrowth structure in layered cathodes is crucial for superior sodium storage performance, stemming from synergistic effects between phases.
• The formation mechanism of these biphasic intergrowth structures remains incompletely understood.

Purpose of the Study:

• To investigate the formation mechanism and electrochemical properties of layered/tunnel intergrowth Na_0.6MnO₂ (LT-NaMO) as a model system.
• To elucidate the role of biphasic intergrowth in enhancing sodium storage performance and structural stability.
• To provide insights into the design of advanced intergrowth cathode materials for SIBs.

Main Methods:

• Synthesis of layered/tunnel intergrowth Na_0.6MnO₂ (LT-NaMO).
• In situ high-temperature X-ray diffraction (HT-XRD) to study structural evolution and thermal stability.
• Electrochemical performance testing, including cycling stability and rate capability.
• Fabrication and testing of a full cell using LT-NaMO cathode and hard carbon anode.

Main Results:

• Successful preparation of the LT-NaMO model material with a layered/tunnel intergrowth structure.
• In situ HT-XRD confirmed the formation process and excellent thermal stability of the intergrowth structure.
• The interlocking effect at phase interfaces significantly mitigated structural strain and lattice volume changes, enhancing cycling stability (∼70.5% capacity retention over 300 cycles at 5C).
• The assembled full cell demonstrated high energy density.

Conclusions:

• The biphasic intergrowth structure, particularly the interlocking effect between layered and tunnel phases, is key to superior electrochemical performance in SIB cathodes.
• Understanding the formation mechanism of intergrowth structures offers valuable guidance for designing high-performance cathode materials for sodium-ion batteries.
• LT-NaMO exhibits promising potential as a cathode material for practical SIB applications.