New Insight on Open-Structured Sodium Vanadium Oxide as High-Capacity and Long Life Cathode for Zn-Ion Storage: Structure, Electrochemistry, and First-Principles Calculation

Herein, the promising properties of open-structured NaV(3)O(8)as a cathode material for Zn-ion batteries (ZIBs) are investigated. First-principles calculations predict the insertion of Zn2+(0.74 angstrom) in NaV(3)O(8)with an interlayer distance of approximate to 7 angstrom, enabling delivery of a high discharge capacity of 353 mAh g(-1)at 70 mA g(-1)(0.2 C) for 300 cycles in the operating window of 0.3-1.5 V in 1mZn(CF3SO3)(2)aqueous solution. Operando synchrotron X-ray diffraction, X-ray absorption near edge structure spectroscopy, and first-principles calculations validate the insertion of Zn(2+)into the NaV(3)O(8)structure within the operation range. Moreover, operando synchrotron X-ray diffraction and operando Raman spectroscopy reveal the formation of layered zinc hydroxytriflate (Zn-5(OH)(8)(CF3SO3)(2)center dot xH(2)O) as a side reaction below 0.8 V on discharge (reduction) and its dissolution into the electrolyte above 0.8 V on charge (oxidation). The formation of the Zn hydroxytriflate interfacial layer increases the charge-transfer activation energy from 15.5 to 48 kJ mol(-1), leading to kinetics fade below 0.8 V. The findings reveal the charge-storage mechanism for NaV3O8, which may also be applicable to other vanadate cathodes, providing new insights for the investigation and design of ZIBs.