Boron-Doping Induced Electron Delocalization in Fluorophosphate Cathode: Enhanced Na-Ion Diffusivity and Sodium-Ion...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium-ion batteries (SIBs) are promising for large-scale energy storage.
• Na3V2(PO4)2O2F (NVPOF) exhibits high specific capacity and working voltage but suffers from slow Na+ diffusivity.
• Structural modifications are crucial for optimizing NVPOF cathode performance.

Purpose of the Study:

• To enhance Na+ diffusivity in NVPOF through boron (B) doping at the phosphorus (P) site.
• To investigate the impact of B-doping on the electronic structure and ionic conductivity of the cathode material.
• To evaluate the electrochemical performance of the B-doped NVPOF cathode in SIBs.

Main Methods:

• Synthesis of Na3V2(P2-xB_xO8)O2F (NVP2-xB_xOF) via B-doping.
• Density functional theory (DFT) modeling to understand electronic structure and ion diffusion.
• Electrochemical characterization including rate capability and cycle stability tests.
• Fabrication and testing of a full cell (NVP1.90B0.10OF//Se-C).

Main Results:

• DFT calculations revealed a reduced bandgap and electron delocalization in NVP2-xB_xOF, lowering electrostatic resistance for Na+.
• Na+ diffusivity was enhanced up to 11 times in the B-doped cathode.
• NVP1.90B0.10OF demonstrated high rate capability (67.2 mAh g-1 at 60 C) and excellent cycle stability (95.9% retention after 1000 cycles at 10 C).
• The full cell achieved high power/energy densities and maintained 90.1% capacity retention after 1000 cycles.

Conclusions:

• Boron doping is an effective strategy to improve Na+ diffusion kinetics in NVPOF cathodes.
• The enhanced cathode material exhibits superior rate performance and long-term stability for SIB applications.
• B-doped NVPOF cathodes hold significant potential for high-performance sodium-ion batteries.