Manipulation of electrochemically (In)active elements in Na₃VMg_0.5Ti_0.5(PO₄)₃ and Na_3.5V_0.5MgTi_0.5(PO₄)₃: Enhancing the longevity of NASICON-type cathodes for sodium-ion batteries

The sodium superionic conductor (NASICON)-type cathode, Na₃V₂(PO₄)₃ (NVP), is considered as a promising cathode material for sodium-ion batteries (SIBs), which offers stable sodium storage capability. However, hazardous and expensive vanadium (V) has limited its practical application. To reduce the V dependency in NASICON-type cathodes, two new NASICON-structured materials, Na₃VMg_0.5Ti_0.5(PO₄)₃ (N_3.0VMTP/C) and Na_3.5V_0.5MgTi_0.5(PO₄)₃ (N_3.5VMTP/C), were designed for cost-effectiveness as well as improvement of battery performance. N_3.0VMTP/C and N_3.5VMTP/C provided a sodium storage capacity of 155.84 mAh g⁻¹ and 105 mAh g⁻¹ at 12 mA g⁻¹ with 88 % and 84 % capacity retention after 500 cycles at 150 mA g⁻¹, respectively. In-situ XRD analysis revealed that both cathodes undergo a progressive solid solution reaction in the lower voltage region and two-phase reaction at higher voltages during (de)sodiation, with only minor difference in the degree of lattice displacement, confirming their high potential for the SIBs with sustainable and cheaper Mg for grid-scale utilization.