Protective effect of ZrO2 coating on Na3V2(PO4)3 to provide cycling stability as cathode for sodium-ion batteries

The study explores the use of Na 3 V 2 (PO 4 ) 3 as a cathode material for sodium-ion batteries, prepared via a citric-based sol-gel method and coated with ZrO 2 using a single impregnation technique. X-ray diffraction confirms the presence of crystalline, highly pure samples, while ZrO 2 remains undetectable due to its low crystallinity and concentration. However, electron microscopy and Raman and X-ray fluorescence spectroscopies reveal a homogeneous ZrO 2 distribution on particle surfaces. Raman spectra indicate a low graphitization level of the amorphous carbon conductive phase. Ex-situ XRD shows that the coating does not affect sodium insertion reversibility, while XPS confirms the participation of the V 4+ /V 3+ redox couples and the sequestration of HF traces by transformation of ZrO 2 into ZrOF 2 . Coatings of 1% and 3% significantly improve capacity at higher rates and reduce direct current resistance, though only the samples coated with 1% maintain capacity after extended cycling at 1C. Cyclic voltammetry and impedance spectroscopy demonstrate that surface capacitance favors fast sodium storage, particularly in ZrO 2 -coated samples. The sample with 1% ZrO 2 exhibits the highest diffusion coefficients, ensuring high-rate capability and cycling stability. Extended cycling tests confirm exceptional capacity retention, validating ZrO 2 coating onto Na 3 V 2 (PO 4 ) 3 as a promising strategy to enhance sodium-ion battery performance.