Construction of Cu 7 KS 4 @Ni x Co 1- x (OH) 2 Nano-Core-Shell Structures with High Conductivity and Multi-Metal Synergistic Effect for Superior Hybrid Supercapacitors.

Reasonable design of materials with complex nanostructures and diverse chemical compositions is of great significance in the field of energy storage. Cu 7 KS 4 (CKS) is considered a potential electrode material for supercapacitors due to its superior electrical conductivity. Transition metal hydroxides are widely used as electrode materials for supercapacitors due to their high theoretical specific capacitance ( C s ); however, single metal species with limited active sites restrict their further applications for energy storage. Herein, through a hydrothermal reaction, CKS nanorods were prepared, and then binary metal hydroxide Ni x Co 1- x (OH) 2 nanosheets were generated directly on CKS nanorods through a one-step hydrothermal reaction to form a nano-core-shell structure (NCSS). By regulating the mole ratio of nickel nitrate to cobalt nitrate, the resulting Ni 0.75 Co 0.25 (OH) 2 nanosheets with the best electrochemical activity were prepared and supported on CKS nanorods to form a CKS@N 0.75 C 0.25 OH NCSS. The as-prepared CKS@N 0.75 C 0.25 OH NCSS has a larger specific surface area, which can provide more active sites, while the abundant metal species composition can generate abundant redox reactions to boost the pseudocapacitance. The prepared CKS@N 0.75 C 0.25 OH/NF electrode exhibits outstanding specific capacitance and cycle life. The assembled CKS@N 0.75 C 0.25 OH/NF//AC all-solid-state asymmetric supercapacitor achieves a high energy density of 88.7 Wh kg -1 at a power density of 849.9 W kg -1 with superior cycle life. Therefore, the use of polymetallic hydroxides to construct NCSS electrodes has great research significance and broad application prospects.