Insights into electrolyte-dependent interfacial chemistry in a high-voltage Na3VFe(PO4)3 cathode through combined experimental and theoretical studies

Abstract

NASICON-type materials are very promising cathodes for sodium-ion batteries (SIBs) owing to their stable 3D framework and rapid Na⁺ diffusion. Although high-voltage Na₃V₂(PO₄)₃ (NVP) has been extensively investigated for good capacity (∼117 mAh g⁻¹) as well as outstanding rate capability, its practical use is limited because of the expensive and toxic vanadium. Hence, replacing V with Fe in Na₃VFe(PO₄)₃ (NVFP) presents a more sustainable composition with dual redox activity while maintaining high voltage. Herein, phase-pure NVFP is synthesized via a facile sol–gel method, delivering a specific capacity of 108.43 mAh g⁻¹ and energy density of ∼317 Wh kg⁻¹ at 0.1C. Furthermore, NVFP demonstrated excellent rate capability with outstanding retention of 88.01% over 100 cycles and 86.11% over 2000 cycles at 0.5C and 3C, respectively. For the first time, NVFP is comprehensively investigated in various carbonate-based electrolytes for the understanding of its influence on Na⁺ diffusion kinetics and overall electrochemical performance. Additionally, the post-cycling analysis and detailed computational study provided crucial insights into the structural stability, diffusion kinetics, and sodium-ion transport mechanisms of NVFP, highlighting its strong potential as a cathode material for future commercialization of SIB systems.