Oxygen-Deficient Organic/Inorganic VOx-PPy cathode composites: Enabling prolonged lifespan of aqueous zinc-ion batteries

Abstract

Service lifespan constitutes a critical factor in the practical application of battery materials. Vanadium oxide cathodes, notwithstanding their high theoretical capacity and redox activity, are commonly regarded as unstable during cycling due to vanadium dissolution. Here we report the remarkable cycling stability of the organic/inorganic composite cathode VO_x-PPy with rich oxygen vacancies. The composite demonstrates an outstanding lifespan with 94 % capacity retention after 20,000 charge/discharge cycles, and a high reversible capacity of 565.5 mAh g⁻¹ at 0.8 A g⁻¹ in a zinc chloride electrolyte. The electrons on the nitrogen atoms of PPy are attracted to the vanadium atoms, resulting in an enhanced protonation of PPy and a reduction in the vanadium oxidation state within VO_x. Owing to the penetration of zinc ions into the PPy main chains, the introduced distortions lead to a decrease in the coplanarity of the aromatic rings and a reduction in the π-conjugation length. However, no significant shifts are observed that would suggest a structural transformation or deformation of PPy after discharging, indicating that the PPy ring skeleton exhibits excellent electrochemical reversibility and stability. Furthermore, the conductive PPy coating can improve electrical conductivity and alleviate vanadium dissolution by acting as a buffer layer. This research highlights the advantages of organic–inorganic composites for Zn²⁺ intercalation and offers valuable perspectives for the development of high-performance aqueous zinc-ion batteries (AZIBs).