Triggering reversible V4+/V5+ redox couples in Na3V2(PO4)3 porous flower-like cathodes by Mg2+ substitution for high-performance Na-ion batteries

Na 3 V 2 (PO 4 ) 3 has received a lot of attention as a prospective cathode for sodium-ion batteries (SIBs) owing to its strong 3D wide-open architecture for Na + transport. However, the practical application is still hampered by its poor electronic conductivity and weak Na + diffusion kinetics . In this paper, a novel Mg 2+ -doped Na 3 V 2 (PO 4 ) 3 flower-like cathode (Na 3+x V 2-x Mg x (PO 4 ) 3 /C, x = 0, 0.02, 0.04, 0.06) with abundant mesoporous has been synthesized by a convenient template-assisted sol-gel method. Mg 2+ doping successfully triggers V 4+ /V 5+ reversible redox with improved voltage plateau and reversible capacity. The hierarchical mesoporous structure combined with carbon layers is beneficial to the fast transport of Na + and e − , which guarantee improved kinetic properties and enhanced conductivity. Attributed to these competitive advantages, significantly improved electrochemical properties of Na 3.04 V 1.96 Mg 0.04 (PO 4 ) 3 /C (NVMP-4) are acquired, including extremely high specific capacity (123.8 mAh g −1 at 1C), excellent rate performance (73.8 mAh·g −1 at 100C) and exceptionally stable energy output with 89.1 % capacity retention after 3000 cycles at 20C. Additionally, when assembled with a hard carbon anode (HC), NVMP-4||HC provides an exceptional energy density of 216.9 Wh kg −1 at 0.2C. By enhancing nanostructure and rational surface engineering, this project offers fresh perspectives for creating superior electrodes, increasing the energy density of SIBs.