Design of Ti⁴⁺/Zr⁴⁺ as Dual-Supporting Sites in Na₃V₂(PO₄)₃ for the Advanced Aqueous Zinc-Ion Battery Cathode

The development of aqueous zinc-ion batteries (AZIBs) still faces a huge challenge due to poor cycling stability and slow kinetics of the cathode material. In this work, we report an advanced cathode of Ti⁴⁺/Zr⁴⁺ as dual-supporting sites in Na₃V₂(PO₄)₃ with an expanded crystal structure, exceptional conductivity, and superior structural stability for AZIBs, which exhibits fast Zn²⁺ diffusion and excellent performance. The results of AZIBs afford remarkably high cycling stability (91.2% retention rate over 4000 cycles) and exceptional energy density (191.3 W h kg^-1), outperforming most Na⁺ superionic conductor (NASICON)-type cathodes. Furthermore, different in/ex situ characterization techniques and theoretical studies reveal the reversible storage mechanism of Zn²⁺ in an optimal Na_2.9V_1.9Ti_0.05Zr_0.05(PO₄)₃ (NVTZP) cathode and demonstrate that Na⁺ defects together with Ti⁴⁺/Zr⁴⁺ sites can intrinsically contribute to the high electrical conductivity and low Na⁺/Zn²⁺ diffusion energy barrier of NVTZP. Moreover, the flexible soft-packaged batteries further demonstrate a superior capacity retention rate of 83.2% after 2000 cycles from the perspective of practicality.