Homo-interface and gradient N-doping cooperation to boost the rate capability of porous NaV8O20·nH2O nanoflake cathode in Zn-ion batteries

Vanadium-based materials are expected to achieve high-rate capability with high energy density in Zn-ion batteries (ZIBs) due to the layered-structure and multi-electron redox mechanism. However, the high-rate charge/discharge capacity is usually restricted by limited charge storage active sites on material surface and poor electrode kinetics. Herein, homo-interfaces and built-in electric fields were constructed to boost the Zn2+ diffusion and electron transmission kinetics of NaV8O20·xH2O (NaVO) nanoflake cathodes, respectively, which cooperated to achieve high-rate charge/discharge capacity in ZIBs. Specifically, firstly, homo-interfacial NaVO nanoflakes were prepared, and then gradient N-doping was introduced from homo-interface to surface of NaVO due to the lower N-doping formation energies of interface than that of surface, which improved electrical conductivity and formed a build-in field to accelerate electron transmission; Moreover, there is a large difference between Zn2+ concentration in homo-interfaces and surfaces of the N-doped NaVO as the homo-interfaces with lower zinc adsorption energy are more conducive to the adsorption and aggregation of Zn2+ than that of the surface, which boost Zn2+ diffusion; Furthermore, numerous micropores were created to shorten ion transport pathways. These structural advantages enabled ultra-fast Zn-storage kinetics and excellent cycling performance of NaV8O20·xH2O in ZIBs, the reversible capacity can reach 417 mA h g−1 at 0.1 A g−1, and as high as ∼110 mA h g−1 at 100 A g−1 with capacity retention of 68.4% after 50,000 cycles. Dynamic analysis verifie that high capacitive capacity contributes most to the excellent performance, which can be ascribed to the structural advantages described above. The findings of this study provide new insights for designing Zn-ion storage materials with high-rate capability and long life.