Aqueous rechargeable batteries present desired properties of considerable energy density, low-cost and high safety for large-scale energy storage systems. However, the scarcity of available negative electrode materials with high capacity and satisfying cycling life still hinders their development. Here, we report a novel tunnel structured KCu7S4 negative electrode material for aqueous rechargeable batteries. The structural evolution and charge storage mechanism of the KCu7S4 is successfully studied by using ex-situ XPS and XRD. The charge storage can be attributed to the deep oxidation of Cu+ into Cu2+/Cu3+ and the good reversible reaction. The electrochemical induced irreversible phase transformation of Cu7S4 into Cu1.96S is mainly responsible for the capacity degradation of the KCu7S4 electrode. Fortunately, the optimized KCu7S4/rGO composite electrode shows good electrochemical performance and the fabricated full cell delivers good energy storage capability. These findings can broaden the horizon of negative elctrode materials and endow new opportunities for the fabrication of advanced rechargeable batteries.
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