Facile Fabrication of Large-Area CuO Flakes for Sodium-Ion Energy Storage Applications

CuO is recognized as a promising anode material for sodium-ion batteries because of its impressive theoretical capacity of 674 mAh g^-1, derived from its multiple electron transfer capabilities. However, its practical application is hindered by slow reaction kinetics and rapid capacity loss caused by side reactions during discharge/charge cycles. In this work, we introduce an innovative approach to fabricating large-area CuO and CuO@Al₂O₃ flakes through a combination of magnetron sputtering, thermal oxidation, and atomic layer deposition techniques. The resultant 2D CuO flakes demonstrate excellent electrochemical properties with a high initial reversible specific capacity of 487 mAh g^-1 and good cycling stability, which are attributable to their unique architectures and superior structural durability. Furthermore, when these CuO flakes are coated with an ultrathin Al₂O₃ layer, the integration of the 2D structures with outer nanocoating leads to significantly enhanced electrochemical properties. Notably, even after 70 rate testing cycles, the CuO@Al₂O₃ materials maintain a high capacity of 525 mAh g^-1 at a current density of 50 mA g^-1. Remarkably, at a higher current density of 2000 mA g^-1, these materials still achieve a capacity of 220 mAh g^-1. Moreover, after 200 cycles at a current density of 200 mA g^-1, a high charge capacity of 319 mAh g^-1 is sustained. In addition, a full cell consisting of a CuO@Al₂O₃ anode and a NaNi_1/3Fe_1/3Mn_1/3O₂ cathode is investigated, showcasing remarkable cycling performance. Our findings underscore the potential of these innovative flake-like architectures as electrode materials in high-performance sodium-ion batteries, paving the way for advancements in energy storage technologies.