Exposed crystal facet regulation of Cu2S/C hollow nanocube anode for high-performance quasi-solid Ni-Cu battery and supercapacitor

Copper sulfides are promising anode materials for aqueous rechargeable devices. However their wide-spread applications have been greatly limited by the rapid activity loss, insufficient structure stability and poor conductivity. Herein, an innovative crystal-facet engineering method has been firstly proposed to remarkably improve the electrochemical reversibility and activity of the anode. And the establishment of the intimate HKUST-1 derived carbon protective layer and the utilization of the gel electrolyte have been simultaneously adopted to optimize the electrochemical reversibility and conductivity of the copper sulfide anode. With the regulation of the dominant exposed facet, the electrode possesses high specific capacitance of 1261.3 F·g−1. The assembled Ni-Cu battery and the hybrid supercapacitor deliver excellent energy densities (56.7 Wh·kg−1 and 16.7 Wh·kg−1) and admirable cycling stabilities (64.9% capacity retention after 2000 cycles and 68.8% capacity retention after 5000 cycles). In addition, the main reason for the cycling stability decay has been investigated in detail. And the density functional theory (DFT) calculations have also completely demonstrated the dramatically positive effects of the exposed facets and carbon covering layer on the improvement of the affinity between the electrode and electrolyte ions, as well as the electrical conductivity.