Rechargeable magnesium batteries (RMBs) are promising candidates for future energy storage due to their intrinsic safety and the low cost of magnesium. A critical challenge for RMBs lies in developing high-performance cathode materials. In this work, to address the structural collapse, volume expansion, and low electrical conductivity of cobalt selenide during cycling, we for the first time successfully prepared Cu-doped ZIF-67 precursors via a precipitation method, which were subsequently sintered to obtain Cu-doped CoSe2 cathode materials. Comparative analysis reveals that Cu doping effectively suppresses structural collapse during electrochemical reactions and mitigates post-sintering degradation at high temperatures. Additionally, Cu doping modulates the density of states, thereby enhancing the electrical conductivity of cobalt selenide. These improvements substantially boost the electrochemical performance of CoSe2. Among the three materials, Co0.98Cu0.02Se2 demonstrates superior properties. It delivers a specific discharge capacity of 106.5 mAh g−1 at 50 mA g−1 and exhibits excellent cycling stability with nearly no capacity decay after 200 cycles. At a high current density of 200 mA g−1, a maximum capacity of 133.8 mAh g−1 is achieved, along with good cycling stability. While excessive Cu doping (4 %) could further increase the specific capacity, it negatively impacts the cycling performance. Further mechanistic investigations using ex-situ X-ray diffraction and X-ray photoelectron spectroscopy elucidate the magnesium storage mechanism. This work highlights the method of Cu doping to enhance the electrochemical performance of CoSe2, which will inspire the design of more doped cathodes in RMBs.
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