Multiple heterostructures, rich oxygen vacancies and expansion counteraction effect co-boosted VO₂/V₂O₃/V₆O₁₃@nitrogen-doped carbon nanosheets as a high-performance cathode for aqueous zinc-ion b

In this study, a novel cathode material comprising VO₂/V₂O₃/V₆O₁₃@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 <i>via</i> a self-sacrificial route utilising an organic-inorganic hybrid layered vanadate precursor, [(CH₃)₂NH₂]V₃O₇. The presence of oxygen vacancies and multiple heterostructures within the cathode facilitates the diffusion of Zn²⁺ 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 (<i>i.e.</i>, positive <i>versus</i> negative expansion) occurs between the VO₂/V₂O₃ and V₆O₁₃ 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^-1, with a remarkable capacity retention rate of 95.6% after 250 cycles at a current density of 0.2 A g^-1. Furthermore, at a high current density of 5 A g^-1, the cathode achieves a maximum discharge capacity of 198.2 mA h g^-1 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.