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

Abstract

AbstractHerein, the promising properties of open‐structured NaV3O8 as a cathode material for Zn‐ion batteries (ZIBs) are investigated. First‐principles calculations predict the insertion of Zn2+ (0.74 Å) in NaV3O8 with an interlayer distance of ≈7 Å, 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 1 m Zn(CF3SO3)2 aqueous solution. Operando synchrotron X‐ray diffraction, X‐ray absorption near edge structure spectroscopy, and first‐principles calculations validate the insertion of Zn2+ into the NaV3O8 structure within the operation range. Moreover, operando synchrotron X‐ray diffraction and operando Raman spectroscopy reveal the formation of layered zinc hydroxytriflate (Zn5(OH)8(CF3SO3)2∙xH2O) 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.