Probing the Ion Dynamics, Structural Changes, and Enhanced Energy Storage of Co ₃ O ₄ Thin Films for Aqueous Zinc-Ion Battery Applications

Recently, aqueous zinc-ion batteries (AZIBs) have been in the spotlight for being safer, more affordable, and more sustainable energy storage devices. However, a high-performance cathode material and its engineering principles are needed for long-lasting applications. This work explores the nanostructure spinel-based metal oxide Co₃O₄ thin film as a cathode for thin-film-based all-solid AZIBs, fabricated via a radio frequency (RF) sputtering technique. The tailored binder and additive-free Co₃O₄ thin-film electrodes exhibit outstanding electrochemical performance, exhibiting remarkable cycling stability for 4000 cycles at a high current density of 50 mA/g, while retaining excellent capacity retention without notable deterioration in the structure. Also, the spinel framework facilitates effective Zn²⁺ diffusion throughout prolonged cycling. Through comprehensive ex situ characterization studies after 500 cycles, including X-ray photoelectron spectroscopy and scanning electron microscopy, we validate the retention of the Co₃O₄ crystal structure with a reversible Zn²⁺ insertion/extraction mechanism throughout the cycling process. Optimized thin films exhibit remarkable specific capacity with outstanding cycling stability performance. This work offers a promising route toward next-generation thin-film-based aqueous ZIBs, through which robust performance can be achieved.