Design of Ti 4+ /Zr 4+ as Dual-Supporting Sites in Na 3 V 2 (PO 4 ) 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 Ti 4+ /Zr 4+ as dual-supporting sites in Na 3 V 2 (PO 4 ) 3 with an expanded crystal structure, exceptional conductivity, and superior structural stability for AZIBs, which exhibits fast Zn 2+ 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 Zn 2+ in an optimal Na 2.9 V 1.9 Ti 0.05 Zr 0.05 (PO 4 ) 3 (NVTZP) cathode and demonstrate that Na + defects together with Ti 4+ /Zr 4+ sites can intrinsically contribute to the high electrical conductivity and low Na + /Zn 2+ 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.