Synergistic interlayer and defect engineering of hydrated vanadium oxide toward stable Zn-ion batteries

• A strategy of interlayer and defect engineering is developed for aqueous ZIBs. • The Ca ions and V vacancies synergistically enhance the Zn-ion storage capability. • The structural stability is enhanced over long-term cycling because of Ca ions. • An outstanding electrochemical performance is achieved over 3000 cycles. Layered hydrated vanadium oxides are considered as promising cathode materials for aqueous Zn-ion batteries because of their open layered frameworks and multiple valence states of vanadium. However, they usually exhibit poor electrochemical performance due to the instability of layered frameworks. Herein, Ca-intercalated hydrated vanadium oxide (CaVO) nanobelts have been synthesized by a simple hydrothermal method, accompanied with the formation of cationic V vacancies. The intercalated Ca ions and induced V vacancies can not only synergistically enhance the Zn-ion storage capability by offering numerous active sites, but also effectively stabilize the crystal structure over long-term cycling because of the pinning effect of Ca ions, leading to the enhanced electrochemical performance of hydrated vanadium oxide. Consequently, the CaVO nanobelts deliver a high reversible capacity of 310 mAh g -1 at a current rate of 0.5 A g -1 , a superior rate performance of 88 mAh g -1 at 15 A g -1 , and an impressive cycling stability with a capacity retention of 91.7% at 10 A g -1 over 3000 cycles. Our present study demonstrates that the synergistic interlayer and defect engineering is a promising strategy to construct advanced layered cathode materials for practical Zn-ion batteries.