Multiple heterostructures, rich oxygen vacancies and expansion counteraction effect co-boosted VO/VO/VO@nitrogen-doped carbon nanosheets as a high-performance cathode for aqueous zinc-ion batteries.

In this study, a novel cathode material comprising VO/VO/VO@nitrogen-doped carbon nanosheets (denoted as VO2/V2O3/V6O13@N-C) with abundant oxygen vacancies was synthesised for aqueous zinc-ion batteries (AZIBs). The synthesis was achieved a self-sacrificial route utilising an organic-inorganic hybrid layered vanadate precursor, [(CH)NH]VO. The presence of oxygen vacancies and multiple heterostructures within the cathode facilitates the diffusion of Zn ions and provides additional active sites for electrochemical reactions. Furthermore, the nanosheet morphology and the nitrogen-doped carbon coating synergistically enhance the electronic conductivity of the cathode. Notably, during the charging and discharging processes, an opposing lattice expansion phenomenon (, positive negative expansion) occurs between the VO/VO and VO phases, leading to an "expansion counteraction" effect that effectively mitigates volumetric changes in the VO2/V2O3/V6O13@N-C cathode. Consequently, the VO2/V2O3/V6O13@N-C cathode exhibits outstanding rate performance and cycling stability. Specifically, the discharge capacity reaches 290.1 mA h g, with a remarkable capacity retention rate of 95.6% after 250 cycles at a current density of 0.2 A g. Furthermore, at a high current density of 5 A g, the cathode achieves a maximum discharge capacity of 198.2 mA h g and retains 86.5% of maximum capacity after 2000 cycles. This study not only proves that calcination of organic-inorganic hybrid layered vanadate is a promising approach for synthesizing high-performance vanadium oxide cathodes, but also presents the "expansion counteraction" strategy to tackle the issue of volume changes for vanadium oxide cathodes.