Rechargeable aluminum batteries (RABs) are a popular energy storage device because of its safety and environmental protection. As cathode materials of RABs, transition metal oxide, sulfide, and selenide have become the research hotspot. In this work, we have successfully prepared CuO, Cu_1.8S, and Cu_1.8Se electrode materials. Among them, although Cu_1.8Se had a relatively higher initial discharge capacity, all of these products had severe capacity degradation in terms of cycling and rate performance. Furthermore, for solving the problem of capacity decline, CMK-3 modified separator was used to make the Cu_1.8Se cathode material more stable, thus improving cycling and rate performance. It can be confirmed by ex situ X-ray photoelectron spectroscopy (XPS) that both Cu and Se elements underwent reversible redox reactions during the charging/discharging process. Density functional theory was implemented to study the energy storage mechanism of Cu_mX (X = O, S, Se). The results showed that Cu_1.8S and Cu_1.8Se mainly relied on AlCl₄⁻ for energy storage, and the intercalation/de-intercalation of Al³⁺ occurred during the charge/discharge process in CuO material. Consequently, the optimized Cu_1.8Se/CMK-3@GF/C/Al revealed an outstanding rate capability (977.83 mAh·g⁻¹ at 0.5 A·g⁻¹) and long cyclic stability (retention of 478.77 mAh·g⁻¹ after 500 cycles at 1.0 A·g⁻¹). Compared to previously reported cathode materials of RABs, this type of battery displays great superiority in terms of rate and cycling stability. This research also provides a novel approach to suppress the shuttle effect of active species for advanced clean energy devices.