High-performance zinc-ion batteries enabled by electrochemically induced transformation of vanadium oxide cathodes

Rechargeable aqueous zinc-ion batteries(ZIBs) have become a research hotspot in recent years,due to their huge potential for high-energy,fast-rate,safe and low-cost energy storage.To realize good electrochemical properties of ZIBs,cathode materials with prominent Zn2+storage capability are highly needed.Herein,we report a promising ZIB cathode material based on electrochemically induced transformation of vanadium oxides.Specifically,K2V6O16·1.5 H2O nanofibers were synthesized through a simple stirring method at near room temperature and then used as cathode materials for ZIBs in different electrolytes.The cathode presented superior Zn2+storage capability in Zn(OTf)2aqueous electrolyte,including high capacity of 321 mAh/g,fast charge/discharge ability(96 mAh/g delivered in 35 s), high energy density of 235 Wh/kg and good cycling performance.Mechanism analysis evidenced that in Zn(OTf)2electrolyte,Zn2+intercalation in the first discharge process promoted K2V6O16·1.5 H2O nanofibers to transform into Zn3+xV2O7(OH)2·2 H2O nanoflakes,and the latter served as the Zn2+-storage host in subsequent charge/discharge processes.Benefiting from open-framework crystal structure and sufficiently exposed surface,the Zn3+xV2O7(OH)2·2H2 O nanoflakes exhibited high Zn2+diffusion coefficient,smaller charge-transfer resistance and good reversibility of Zn2+intercalation/de-intercalation,thus leading to superior electrochemical performance.While in ZnS04 aqueous electrolyte,the cathode material cannot sufficiently transform into Zn3+xV2O7(OH)2·2 H2O thereby corresponding to inferior electrochemical behaviors.Underlying mechanism and influencing factors of such a transformation phenomenon was also explored.This work not only reports a high-performance ZIB cathode material based on electrochemically induced transformation of vanadium oxides,but also provides new insights into Zn2+-storage electrochemistry.