Cu²⁺ substitution regulating Na₃V₂(PO₄)₃ with solid SEI membrane for superior electrochemical performance.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-ion batteries (SIBs) are promising for grid-scale energy storage.
• Na3V2(PO4)3 (NVP) is a potential cathode material but suffers from poor ionic and electronic conductivity.
• Improving conductivity is crucial for high-performance SIB cathodes.

Purpose of the Study:

• To enhance the electrochemical performance of Na3V2(PO4)3 (NVP) for sodium-ion batteries.
• To address the limitations of poor ionic and electronic conductivity in NVP.
• To introduce a novel dual-optimization strategy using Cu2+ doping and carbon nanotube (CNT) wrapping.

Main Methods:

• Synthesized Cu2+ doped NVP with a Na-rich composition (Na3+xV2-yCuy(PO4)3).
• Wrapped the doped NVP particles with tubular carbon nanotubes (CNTs).
• Characterized the material's structure, morphology, and electrochemical properties, including *in situ* EIS measurements.

Main Results:

• Cu2+ doping at V3+ sites improved electronic conductivity via p-type doping and expanded Na+ migration channels.
• The Na-rich scheme provided more active Na+ and maintained charge integrity.
• CNTs formed a conductive framework, enhancing electron transfer and increasing active material-electrolyte contact.
• The optimized Na3.07V1.93Cu0.07(PO4)3@CNTs cathode exhibited excellent rate capability, delivering 124.2 mAh g-1 at 0.1 C and 101.9 mAh g-1 at 10 C.
• Stable SEI formation was confirmed, ensuring electrode stability.

Conclusions:

• The dual-optimization strategy of Cu2+ doping and CNT wrapping effectively enhances the ionic and electronic conductivity of NVP.
• The Na-rich Cu-doped NVP@CNTs material demonstrates superior rate capability and stability for sodium-ion battery applications.
• This approach offers a promising pathway for developing high-performance cathode materials for next-generation energy storage systems.