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/Zr as dual-supporting sites in NaV(PO) with an expanded crystal structure, exceptional conductivity, and superior structural stability for AZIBs, which exhibits fast Zn 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), 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 in an optimal NaVTiZr(PO) (NVTZP) cathode and demonstrate that Na defects together with Ti/Zr sites can intrinsically contribute to the high electrical conductivity and low Na/Zn 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.