Enhanced Electrochemical Performance of Na₃V_1.5Cr_0.4Fe_0.1(PO₄)₃ NASICON Cathode for High-Rate Sodium-Ion

The increasing demand for sustainable energy storage systems has drawn significant attention to sodium-ion batteries (SIBs) as a viable alternative to lithium-ion batteries, due to the abundance and low cost of sodium resources. One of the key challenges in SIB development is the improvement of cathode materials, which typically suffer from lower ionic mobility and electronic conductivity. In this study, we developed a NASICON-structured Na₃V_1.5Cr_0.4Fe_0.1(PO₄)₃ (NVCFP) cathode material by dual-doping vanadium phosphate (Na₃V₂(PO₄)₃, NVP) with chromium (Cr) and iron (Fe). The dual-doping strategy significantly enhances the electrochemical performance of the material, particularly its high-rate capability and cycling stability.<br/>NVCFP exhibited a discharge capacity of 71 mAh g^-1 at a high current rate of 100 C and retained 95% of its initial capacity after 10,000 cycles. The improved performance is attributed to the synergistic effects of Cr and Fe co-doping, which enhance both structural stability and electronic conductivity. Cr doping facilitates a reversible V³⁺/V⁵⁺ redox reaction at high voltage, improving the stability of the NASICON framework, while Fe doping introduces new electronic conduction pathways, boosting the overall conductivity of the material. Rietveld refinement and synchrotron X-ray diffraction (XRD) confirmed the successful incorporation of Cr and Fe into the crystal structure without compromising the phase purity of the material.<br/>Density functional theory (DFT) calculations and electrochemical impedance spectroscopy (EIS) showed that NVCFP has lower charge-transfer resistance and improved Na⁺ ion diffusion kinetics compared to undoped NVP. The material also demonstrated a lower energy barrier for Na⁺ ion migration, contributing to its enhanced high-rate performance. Cyclic voltammetry (CV) results further indicated that NVCFP has a high pseudocapacitive contribution, particularly at high scan rates, making it suitable for high-power applications.<br/>In full-cell configurations with a hard carbon anode, NVCFP demonstrated superior initial discharge capacity and cycling stability compared to undoped NVP. These findings highlight the potential of Na₃V_1.5Cr_0.4Fe_0.1(PO₄)₃ as a high-performance cathode material for sodium-ion batteries, offering a promising pathway for the development of large-scale, cost-effective energy storage systems.<br/><br/>1. Yang, A.; Huang, X.; Luo, C.; Wang, H.; Zhou, T. High-Rate-Capacity Cathode Based on Zn-Doped and Carbonized Polyacrylonitrile-Coated Na₄MnV(PO₄)₃ for Sodium-Ion Batteries. <i>ACS Appl. Mater. Interface</i> <b>2023</b>, <i>15</i>, 22132– 22141.<br/>2. Soundharrajan, V.; Nithiananth, S.; Sakthiabirami, K.; Kim, J. H.; Su, C.-Y.; Chang, J.-K. The Advent of Manganese-Substituted Sodium Vanadium Phosphate-Based Cathodes for Sodium-Ion Batteries and their Current Progress: A Focused Review. <i>J. Mater. Chem. A</i> <b>2022</b>, <i>10</i>, 1022– 1046.<br/>3. Castelvecchi,D. Electric Cars and Batteries: How will the World Produce Enough?. <i>Nature</i> <b>2021</b>, <i>596</i>, 336– 339.<br/>4. Scrosati, B.; Hassoun, J.; Sun, Y.-K. Lithium-ion batteries. A Look into the Future. <i>Energy Environ. Sci.</i> <b>2011</b>, <i>4</i>, 3287– 3295.<br/>5. Vaalma, C.; Buchholz, D.; Weil, M.; Passerini, S. A cost and resource analysis of sodium-ion batteries. <i>Nat. Rev.</i> <b>2018</b>, <i>3</i>, 18013.