High-performance Zn-ion batteries constructed by in situ conversion of surface-oxidized vanadium nitride into Zn 3 (OH) 2 V 2 O 7 ·2H 2 O with oxygen defects

Herein, surface-oxidized vanadium nitride (O-VN) is synthesized by a one-step hydrothermal method without multi-step reactions, and is applied as a cathode material for aqueous zinc ion batteries. After in situ electrochemical activation, it turns into Zn 3 (OH) 2 V 2 O 7 ·2H 2 O with copious oxygen vacancies/defects. The electrochemical phase transition and in situ defect induction can provide abundant active sites for the storage of Zn 2+ , thus increasing the energy storage performance of electrode materials. As expected, Zn 3 (OH) 2 V 2 O 7 ·2H 2 O with oxygen defects has good structural and morphological stability during cycling, and exhibits excellent specific capacity (510 mA h g −1 at 0.1 A g −1 and 199 mA h g −1 at 10 A g −1 ) and superior cycle stability (72.6% capacity retention after 3000 cycles at 20 A g −1 ).