Construction of Dense Cu ₂ O Microsphere Structures on Current Collector Surfaces for High-Performance Anode-Free Aqueous Zinc-Ion Batteries

Anode-free aqueous zinc-ion batteries (AF-AZIBs) enhance energy density by eliminating the traditional thick zinc foil anode. However, they often face challenges such as low Coulombic efficiency (CE) and unstable cycling performance, primarily caused by uneven zinc deposition and dendrite growth on the current collector. To address these issues, we propose a simple, cost-effective surface modification method for Cu foil as the anode current collector. We brush the Cu foil surface with a marker pen filled with a mixed solution of (NH₄)₂S₂O₈ and NaOH, enabling the in situ formation of dense Cu₂O microspheres (Dense-Cu₂O@Cu). This method offers better control over microsphere formation in comparison to conventional direct immersion methods, resulting in a uniform and dense microsphere structures. The dense microspheres increase the specific surface area and active site density, promoting more uniform zinc deposition, suppressing dendrite growth, and enhancing CE. Zn||Dense-Cu₂O@Cu half cells exhibit stable cycling performance for over 4000 cycles at 5 mA cm^-2 with CE > 99.9%. Full cells with Dense-Cu₂O@Cu as the anode and pregalvanized vanadium dioxide (ZnVO) as the cathode exhibit an initial capacity of 329 mAh g^-1 at 0.5 A g^-1. They retain 80.6% of their initial capacity after 1000 cycles. This efficient interfacial engineering offers valuable insights into advancing high-performance AF-AZIBs.