Single-Crystalline Biphasic Layered Cathodes for Sodium-Ion Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• O3-type layered cathodes offer high capacity for sodium-ion batteries.
• Structural degradation and performance loss occur during cycling due to phase transitions.
• A need exists for stable cathode materials to enhance sodium-ion battery longevity.

Purpose of the Study:

• To design and synthesize single-crystalline O3/P2 biphasic layered cathodes (O3/P2-NNMO).
• To investigate the structural and electrochemical properties of the novel O3/P2-NNMO cathodes.
• To enhance the cycling stability and rate capability of sodium-ion batteries.

Main Methods:

• A facile solvent-regulated strategy was employed for material synthesis.
• Comprehensive characterization techniques were used to analyze structural and chemical properties.
• Electrochemical performance was evaluated through charge/discharge cycling and rate capability tests.

Main Results:

• The O3/P2-NNMO cathodes exhibited favorable surface chemistry with low residual sodium and high Mn⁴⁺/Mn³⁺ proportion.
• An interlock structure formed between O3 and P2 phases within single particles, reducing lattice variation and phase transitions.
• High reversible capacity (117.2 mAh g^-1 at 0.1 C) and excellent cycling stability (75% retention after 100 cycles at 1 C) were achieved.
• Enhanced Na⁺ diffusion kinetics and interfacial charge transfer led to superior rate capability.

Conclusions:

• The single-crystalline O3/P2 biphasic structure effectively mitigates structural degradation in layered cathodes.
• The O3/P2-NNMO cathodes demonstrate significant potential for high-performance sodium-ion batteries.
• This work offers a novel design strategy for developing advanced layered cathode materials.